c 0hd DemonoidSee {Demonoid}.101Found by Achim Flammenkamp in August 1994. The name was suggested by Bill Gosper, noting that the {phase} shown below displays the period in binary.p5@                  10hd DemonoidSee {Demonoid}. 119P4H1V0qA {spaceship} discovered by Dean Hickerson in December 1989, the first spaceship of its kind to be found. Hickerson then found a small {tagalong} for this spaceship which could be attached to one side or both. These three variants of 119P4H1V0 were the only known c/4 orthogonal spaceships until July 1992 when Hartmut Holzwart discovered a larger spaceship, 163P4H1V0.c/4 orthogonallyp4w! "       !  !                      !       !  "!#1-2-3Found by Dave Buckingham, August 1972. This is one of only three essentially different p3 {oscillator}s with only three cells in the {rotor}. The others are {stillater} and {cuphook}.p3   1-2-3-4See also {Achim's p4}.p4      135-degree MWSS-to-GThe following {converter}, discovered by Matthias Merzenich in July 2013. It accepts an {MWSS} as input, and produces an output {glider} travelling at a 135-degree angle relative to the input direction.               14-ner= {fourteener}17c/45 spaceshipA {spaceship} travelling at seventeen forty-fifths of the {speed of light}. This was the first known {macro-spaceship} speed. See {Caterpillar} for details.180-degree kickbackThe only other two-{glider} collision besides the standard {kickback} that produces a clean output glider with no leftover {ash}. The 180-degree change in direction is occasionally useful in {glider synthesis}, but is rarely used in {signal} circuitry or in {self-supporting} patterns like the {Caterpillar} or {Centipede}, because 90-degree collisions are generally much easier to arrange. 1G seed See {seed}.(2,1)c/6 spaceshipA {knightship} that travels obliquely at the fastest possible speed. To date the only known example of a spaceship with this velocity is {Sir Robin}.(23,5)c/79 Herschel climberThe following glider-supported {Herschel climber} reaction used in the {self-supporting} {waterbear} {knightship}, which can be repeated every 79 ticks, moving the {Herschel} 23 cells to the right and 5 cells upward, and releasing two {glider}s to the northwest and southwest. As the diagram shows, it is possible to substitute a loaf or other {still life}s for some or all of the support gliders. This fact is used to advantage at the front end of the waterbear.! " #!"  $24-cell quadratic growthA 39786x143 {quadratic growth} pattern found by Michael Simkin in October 2014, two days after {25-cell quadratic growth} and a week before {switch-engine ping-pong}.25-cell quadratic growthA 25-cell quadratic growth pattern found by Michael Simkin in October 2014, with a bounding box of 21372x172. It was the smallest-population quadratic growth pattern for two days, until the discovery of {24-cell quadratic growth}. It superseded {wedge}, which had held the record for eight years. See {switch-engine ping-pong} for the lowest-population {superlinear growth} pattern as of July 2018, along with a list of the record-holders. 25P3H1V0.1vA {spaceship} discovered by Dean Hickerson in August 1989. It was the first c/3 spaceship to be discovered. In terms of its 25 cells, it is tied with {25P3H1V0.2} as the smallest c/3 spaceship. Unlike 25P3H1V0.2, it has a population of 25 in all of its phases, as well as a smaller bounding box. Martin Grant discovered a glider synthesis for 25P3H1V0.1 on 6 January 2015.c/3 orthogonallyp3        25P3H1V0.2A {spaceship} discovered by David Bell in early 1992, with a minimum of 25 cells - the lowest number of cells known for any c/3 spaceship. A note in {Spaceships in Conway's Life} indicates that it was found with a search that limited the number of live cells in each column, and possibly also the maximum cross-section (4 cells in this case). See also {edge-repair spaceship} for a very similar c/3 spaceship with a minimum population of 26. In December 2017 a collaborative effort found a 26-glider synthesis for this spaceship.c/3 orthogonallyp3       26-cell quadratic growth = {wedge}. 295P5H1V1_The first {spaceship} of its type to be discovered, found by Jason Summers on 22 November 2000.c/5 diagonallyp5'                                                         !"#$% $  "$& &'!$%&!*    & ' + !!!&!'!+!"")"#'#$$$$&$)$%%(%)%*%&&& &!&$&(&,&.&/&' '!'#')'-'0'%(&()(-(")$)%)')()*)-).)2)*%*)*1*3* +!+.+/+3+&,.,/,'-(-)---.-1-&.).+.,.-.&/+/,/'0*1-1)2*3+3442c/3Two thirds of the speed of light - the speed of signals in a {2c/3 wire} or of some {against the grain} {negative spaceship} signals in the {zebra stripes} {agar}, and also the speed of {burn}ing of the {blinker fuse} and the {bi-block fuse}. 2c/3 wireTA {wire} discovered by Dean Hickerson in March 1997, using his {dr} {search program}. It supports {signal}s that travel through the wire diagonally at two thirds of the {speed of light}. Each 2c/3 signal is made up of two half-signals that can be separated from each other by an arbitrary number of {tick}s. Considerable effort has been spent on finding a way to turn a 2c/3 signal 90 or 180 degrees, since this would by one way to prove Life to be {omniperiodic}. There is a known 2c/3 converter shown under {signal elbow}, which converts a standard 2c/3 signal into a double-length signal. This is usable in some situations, but unfortunately it fails when its input is a double-length signal, so it can't be used to complete a loop. Noam Elkies discovered a glider synthesis of a reaction that can repeatably insert a signal into the upper end of a 2c/3 wire. See {stable pseudo-Heisenburp} for details. On 11 September 2017, Martin Grant reduced the input reaction to five gliders, or three gliders plus a {Herschel}. With the Herschel option the {recovery time} is 152 ticks. See also {5c/9 wire}.                                    ! ! !"#$ !"#$'"#$%&' ! !!!!$!%!&!'!(!)!!"#"*"!###&#'#(#)#*#"$#$%$-$%%(%)%*%+%,%-%%&'&$'%'''*'+','-'.'/''()(0('))),)-).)0)(*)*+*/*++.++,-,*-+---/-../.1/2c/5 spaceship#A {spaceship} travelling at two fifths of the {speed of light}. The only such spaceships that are currently known travel orthogonally. Examples include {30P5H2V0}, {44P5H2V0}, {60P5H2V0}, and {70P5H2V0}. As of June 2018, only 30P5H2V0 and 60P5H2V0 have known {glider synthesis} {recipe}s.2c/7 spaceshipA {spaceship} travelling at two sevenths of the {speed of light}. The only such spaceships that are currently known travel orthogonally. The first to be found was the {weekender}, found by David Eppstein in January 2000. See also {weekender distaff}.2 eaters= {two eaters}2-engine CordershipThe smallest known Cordership, with a minimum population of 100 cells, discovered by Aidan F. Pierce on 31 December 2017. Luka Okanishi produced a 9-glider synthesis of the spaceship on the same day.d       '('( ''(()***++,...////00)12-glider collisionTwo gliders can react with each other in many different ways, either at right angles, or else head-on. A large number of the reactions cleanly destroy both gliders leaving nothing. Many of the remaining reactions cleanly create some common objects, and so are used as the first steps in {glider synthesis} or as part of constructing interesting objects using {rake}s. Only a small number of collisions can be considered {dirty} due to creating multiple objects or a mess. Here is a list of the possible results along with how many different ways they can occur (ignoring reflections and rotations). ------------------------------- result right-angle head-on ------------------------------- nothing 11 17 {beehive} 1 0 {B-heptomino} 1 2 {bi-block} 1 0 {blinker} 2 1 {block} 3 3 {boat} 0 1 {eater1} 1 0 {glider} 1 1 {honey farm} 3 2 {interchange} 1 0 {loaf} 0 1 {lumps of muck} 1 0 {octomino} 0 1 {pi-heptomino} 2 1 {pond} 1 1 {teardrop} 1 0 {traffic light} 2 1 {four skewed blocks} 0 1 {dirty} 6 0 ------------------------------- The messiest of the two-glider collisions in the "dirty" category is {2-glider mess}. 2-glider messA constellation made up of eight {blinker}s, four {block}s, a {beehive} and a {ship}, plus four emitted {glider}s, created by the following {2-glider collision}. Two of the blocks, two of the gliders, and the ship are the standard signature {ash} of a {Herschel}.       30P5H2V0A spaceship discovered by Paul Tooke on 7 December 2000. With just 30 cells, it is currently the smallest known 2c/5 spaceship. A {glider synthesis} for 30P5H2V0 was found by Martin Grant in January 2015, based on a predecessor by Tanner Jacobi.2c/5 orthogonallyp5         31c/240The rate of travel of the {31c/240 Herschel-pair climber} reaction, and {Caterpillar}-type spaceships based on that reaction. Each {Herschel} travels 31 cells orthogonally every 240 {tick}s.31c/240 Herschel-pair climberThe mechanism defining the rate of travel of the {Centipede} and {shield bug} spaceships. Compare {pi climber}. It consists of a pair of {Herschel}s climbing two parallel chains of blocks. Certain spacings between the block chains allow gliders from each Herschel to delete the extra ash objects produced by the other Herschel. Two more gliders escape, one to each side, leaving only an exact copy of the original block chains, but shifted forward by 9 cells:';<;<;<  ; < 72829273:374:46575859566 666767578886869=:3c/7 spaceshipA {spaceship} travelling at three sevenths of the {speed of light}. The only such spaceships that are currently known travel orthogonally. The first to be found was the {spaghetti monster}, found by Tim Coe in June 2016.3-engine CordershipSee {Cordership}.44P5H2V0@A {spaceship} discovered by Dean Hickerson on 23 July 1991, the first 2c/5 spaceship to be found. Small {tagalong}s were found by Robert Wainwright and David Bell that allowed the creation of arbitrarily large 2c/5 spaceships. These were the only known 2c/5 spaceships until the discovery of {70P5H2V0} in December 1992.2c/5 orthogonallyp5,                     45-degree LWSS-to-G= {45-degree MWSS-to-G}.45-degree MWSS-to-GThe following small {converter}, which accepts an MWSS or LWSS as input and produces an output glider travelling at a 45-degree angle relative to the input direction.K                       4-8-12 diamond&The following {pure glider generator}.$      4 boatsp24FD= {Fast Forward Force Field}. This term is no longer in common use.4g-to-5g reactionA reaction involving 4 gliders which cleanly produces 5 gliders. The one shown below was found by Dieter Leithner in July 1992: The first two gliders collide to produce a {traffic light} and glider. The other two gliders react symmetrically with the evolving {traffic light} to form four gliders. A {glider gun} can be built by using {reflector}s to turn four of the output gliders so that they repeat the reaction.+*+*,-56P6H1V0zA 56-cell {spaceship} discovered by Hartmut Holzwart in 2009, the smallest known c/6 orthogonal spaceship as of July 2018.c/6 orthogonallyp68                     58P5H1V1A {spaceship} discovered by Matthias Merzenich on 5 September 2010. In terms of its minimum population of 58 cells it is the smallest known c/5 diagonal spaceship. It provides sparks at its trailing edge which can perturb gliders, and this property was used to create the first c/5 diagonal puffers. These sparks also allow the attachment of tagalongs which was used to create the first c/5 diagonal wickstretcher in January 2011.c/5 diagonallyp5:      5c/9 wireA {wire} discovered by Dean Hickerson in April 1997, using his {dr} {search program}. It supports {signal}s that travel through the wire diagonally at five ninths of the {speed of light}. See also {2c/3 wire}.                                                             !!" !"%!"#$% &'!#$&(!#%(!#(*+ !#$'(+   % ) !!!!! !!!"!#!$!&!'!(!,!""$"&")"*"+","##"#&#(#/#$$$!$#$$$%$&$($+$,$-$.$/$%%!%(%*%0%1%!&#&$&%&&&(&+&-&.&0&3&!'#'&'(')'+'-'/'2'3' (!($('(+(-(")#)()))*)+)-).)"*&*(*/*#+$+%+&+(+*+++,+-+.+0+',),.,0,%-)-,-0-1-%.&.).+.-.../.2.(/)/+/1/,0.0/000-1.14260P3129Found by Dave Greene, 1 November 2004, based on {92P156}.p312< !       #!"#()() #"$ " $ !#! " ""# ### $ $(())**60P5H2V0A 60-cell {spaceship} discovered by Tim Coe in May 1996. It was the first non-c/2 orthogonal spaceship to be successfully constructed via {glider synthesis}.2c/5 orthogonallyp5<                      67P5H1V1A {spaceship} discovered by Nicolay Beluchenko in July 2006. It was the smallest known c/5 diagonal spaceship until the discovery of {58P5H1V1} in September 2010.c/5 diagonallyp5C                   70P5H2V0@A {spaceship} discovered by Hartmut Holzwart on 5 December 1992.2c/5 orthogonallyp5F                        7x9 eater"A high-{clearance} {eater5} variant that can suppress passing gliders in tight spaces, such as on the inside corner of an {R64} {Herschel conduit}. Like the eater5 and {sidesnagger}, the 7x9 eater is able to eat gliders coming from two directions, though this ability is not commonly used.%                83P7H1V1 = {lobster}86P5H1V1A {spaceship} discovered by Jason Summers on January 8, 2005. It was the smallest known c/5 diagonal spaceship until the discovery of {67P5H1V1} in July 2006.c/5 diagonallyp5V                                      90-degree kickbackSee {kickback reaction}.92P156Discovered by Jason Summers on October 31, 2004. It is actually an eight-barrel {glider gun}, with all output gliders suppressed by {eater1}s. Replacing each pair of eater1s with a {beehive} doubles the period and produces {60P312}.p156\  !       $    " # $  !   ! " #!"#()() !"!    " # $ ! ! !!!!$! " """ " ### #$ $ $!$(())**9hdSeparated by 9 {half diagonal}s. Specifically used to describe the distance between the two {construction lane}s in the {linear propagator}. Achim's p144SThis was found (minus the blocks shown below) on a cylinder of width 22 by Achim Flammenkamp in July 1994. Dean Hickerson reduced it to a finite form using {figure-8}s the same day. The neater finite form shown here, replacing the figure-8s with blocks, was found by David Bell in August 1994. See {factory} for a use of this oscillator.p144*           Achim's p16&Found by Achim Flammenkamp, July 1994.p16                 Achim's p4 Dave Buckingham found this in a less compact form (using two halves of {sombreros}) in 1976. The form shown here was found by Achim Flammenkamp in 1988. The {rotor} is two copies of the rotor of {1-2-3-4}, so the oscillator is sometimes called the "dual 1-2-3-4".p4(         Achim's p5= {pseudo-barberpole} Achim's p8&Found by Achim Flammenkamp, July 1994.p8 acornA {methuselah} found by Charles Corderman. It has a final population of 633 and covers an area of 215 by 168 cells, not counting the 13 gliders it produces. Its {ash} consists of typical stable objects and blinkers, along with the relatively rare {mango} and a temporary {eater1}.stabilizes at time 5206 A for all&Found by Dean Hickerson in March 1993.p6    against the grainA term used for {negative spaceship}s travelling in {zebra stripes} agar, perpendicular to the stripes, and also for {against-the-grain grey ship}s. Below is a sample {signal}, found by Hartmut Holzwart in April 2006, that travels against the grain at {2c/3}. This "negative spaceship" travels upward and will quickly reach the edge of the finite patch of stabilized agar shown here. Holzwart proved in 2006 that 2c/3 is the maximum speed at which signals can move non-destructively against the grain through zebra stripes agar.H !      !"#$      !"#      !"#$      !"#                          ! " # $                           ! " #                           ! " # $      !"#      !"#$      !"#      !"#$     !"#       !"#$      !"#   !"#  $ !"#    !!!!!!!! !!!!!!! !!!"!#!" """"""""$"######## # # ######### #!#"### $ $$$$$%%%%%%% % % %%%%%%%%%% %!%"%#%&&&&&&&$&''''' ' ''''''' '!'"'#'( ((())))))))) )!)")#)** * ********$*+++++++++++++++++ +!+"+#+ , ,,,,,,,-------- - -------- -!-"-#-. ..$.//////// / / / / /////////////// /!/"/#/000011111111 1 1 1 1 11111111111111111 1!1"1#12$233333333 3 3 3 3 3333333333333333333 3!3"3#344 4 4444444!4%5against-the-grain grey shipA {grey ship} in which the region of density 1/2 consists of lines of ON cells lying perpendicular to the direction in which the spaceship moves. See also {with-the-grain grey ship}.agar!Any pattern covering the whole plane that is periodic in both space and time. The simplest (nonempty) agar is the {stable} one extended by the known {spacefiller}s. For some more examples see {chicken wire}, {houndstooth agar}, {onion rings}, {squaredance} and {Venetian blinds}. Tiling the plane with the pattern O......O produces another interesting example: a p6 agar which has a phase of {density} 3/4, which is the highest yet obtained for any phase of an oscillating pattern. See {lone dot agar} for an agar composed of isolated cells.aircraft carrierBThis is the smallest {still life} that has more than one {island}.p1airforcejFound by Dave Buckingham in 1972. The rotor consists of two copies of that used in the {burloaferimeter}.p7*                     AK47 reaction;The following reaction (found by Rich Schroeppel and Dave Buckingham) in which a honey farm predecessor, catalysed by an eater and a block, reappears at another location 47 generations later, having produced a glider and a traffic light. This was in 1990 the basis for the Dean Hickerson's construction of the first {true} p94 gun, and for a very small (but {pseudo}) p94 glider gun found by Paul Callahan in July 1994. (The original true p94 gun was enormous, and has now been superseded by comparatively small {Herschel loop} guns and Mike Playle's tiny {AK94 gun}.)     AK94 gunoThe smallest known gun using the {AK47 reaction}, found by Mike Playle in May 2013 using his {Bellman} program.g    #$"% #$!"""$%  " %    " #      & Al Jolson = {Jolson}almost knightshipA promising {partial result} discovered by Eugene Langvagen in March 2004. This was an early near miss in the ongoing search for a small {elementary} (2,1)c/6 {knightship}. After six generations, only two cells are incorrect.C                      almosymmetricFound in 1971.p2  ambidextrousA type of {Herschel transceiver} where the {receiver} can be used in either of two mirror-image orientations. See also {chirality}.anteaterA pattern that consumes {ants}. Matthias Merzenich discovered a c/5 anteater on 15 April 2011. See {wavestretcher} for details.antlers= {moose antlers}ants-The standard form is shown below. It is also possible for any ant to be displaced by one or two cells relative to either or both of its neighbouring ants. Dean Hickerson found {fencepost}s for both ends of this wick in October 1992 and February 1993. See {electric fence}, and also {wickstretcher}.p5 wickH #$()   !%&*+   !%&*+  #$(), antstretcherAny {wickstretcher} or {wavestretcher} that stretches {ants}. Nicolay Beluchenko and Hartmut Holzwart constructed the following small {extensible} antstretcher in January 2006:6756/06./56057:;2378:;<=23>>8: ; : ; < 9 : =  ; !567: !589: !$&'89$()+,679:#()-.019: "#&'-.2357#+,23!"016 !5       !!"##$$$ %%% & &&&&'''(( ) ) ))) * *** + ++, , ,-- - -./ / 0 0112222233 3445 5?6anvilThe following {induction coil}. apgluxeSee {apgsearch}apgmeraSee {apgsearch}.apgnanoSee {apgsearch}. apgsearchOne of several versions of a client-side Ash Pattern Generator {soup} search script by Adam P. Goucher, for use with Conway's Life and a wide variety of other rules. Development of the original {Golly}-based Python script started in August 2014. After the addition in 2016 of apgnano (native C++) and apgmera (self-modifying, 256-bit SIMD compatibility), development continues in 2017 with apgluxe (Larger Than Life and Generations rules, more soup shapes). Several customized variants of the Python script have also been created by other programmers, to perform types of searches not supported by Goucher's original apgsearch 1.x. All of these versions of the search utility work with a "haul" that usually consists of many thousands or millions of random soup patterns. Each soup is run to stability, and detailed object {census} results are reported to {Catagolue}. For any rare objects discovered in the {ash}, the source soup can be easily retrieved from the Catagolue server.APPSAn asymmetric {PPS}. The same as the {SPPS}, but with the two halves 15 generations out of phase with one another. Found by Alan Hensel in May 1998.c/5 orthogonallyp30arkA pair of mutually stabilizing {switch engine}s. The archetype is {Noah's ark}. The diagram below shows an ark found by Nick Gotts that takes until generation 736692 to stabilize, and can therefore be considered as a {methuselah}. armA long extension, sometimes also called a "wing", hanging off from the main body of a {spaceship} or {puffer} perpendicular to the direction of travel. For example, here is a sparking c/3 spaceship which contains two arms. Many known spaceships have multiple arms, usually fairly narrow. This is an artefact of the search methods used to find such spaceships, rather than an indication of what a "typical" spaceship might look like. For an alternate meaning see {construction arm}.r                                          armlessA method of generating {slow salvo}s across a wide range of lanes without using a {construction arm} with a movable {elbow}. Instead, streams of gliders on two fixed opposing {lane}s collide with each other to produce clean 90-degree output gliders. Slowing down one of the streams by 8N ticks will move the output lanes of the gliders toward the source of that stream by N {full diagonal}s. This construction method was used to create the supporting slow salvos in the {half-baked knightship}s, and also in the {Parallel HBK gun}.ashThe {stable} or oscillating objects left behind when a chaotic reaction stabilizes, or "burns out". Experiments show that for random {soup}s with moderate initial densities (say 0.25 to 0.5) the resulting ash has a density of about 0.0287. (This is, of course, based on what happens in finite fields. In infinite fields the situation may conceivably be different in the long run because of the effect of certain initially very rare objects such as {replicator}s.) asynchronousIndicates that precise relative timing is not needed for two or more input {signal}s entering a {circuit}, or two or more sets of {glider}s participating in a {glider synthesis}. In some cases the signals or sets of gliders can arrive in any order at all - i.e., they have non-overlapping effects. However, in some cases such as {slow salvo} constructions, there is a required order for some of the incoming signals. These signals can still be referred to as "asynchronous" because the number of ticks between them is infinitely adjustable: arbitrarily long delays can be added with no change to the final result. Compare {synchronized}.aVeragepFound by Dave Buckingham, 1973. The average number of live {rotor} cells is five (V), which is also the period.p5*         B= {B-heptomino}B29The following {spaceship}, found by Hartmut Holzwart in April 2004. A glider synthesis of this spaceship was completed by Tanner Jacobi in April 2015.c/4 diagonallyp4"             B-52 bomberThe following p104 {double-barrelled} {glider} {gun}. It uses a {B-heptomino} and emits one glider every 52 generations. It was found by Noam Elkies in March 1996, except that Elkies used {blocker}s instead of {mold}s, the improvement being found by David Bell later the same month.U"$!  "%  "$&#&$%      $ % $ %   #$#$&&&#&$%'B60bA {Herschel conduit} discovered by Michael Simkin in 2015 using his search program, {CatForce}. It is one of two known {Blockic} {elementary conduit}s. After 60 ticks, it produces a Herschel rotated 180 degrees at (-6,-10) relative to the input. It can most easily be connected to another B60 conduit, producing a closed loop, the {Simkin glider gun}.           babbling brookAny {oscillator} whose {rotor} consists of a string of cells each of which is adjacent to exactly two other rotor cells, except for the endpoints which are adjacent to only one other rotor cell. Compare {muttering moat}. Examples include the {beacon}, the {great on-off}, the {light bulb} and the {spark coil}. The following less trivial example (by Dean Hickerson, August 1997) is the only one known with more than four cells in its rotor. It is p4 and has a 6-cell rotor..                  backrake}Another term for a backwards {rake}. A p8 example by Jason Summers is shown below. See {total aperiodic} for a p12 example.X                               backward gliderzA {glider} which moves at least partly in the opposite direction to the {puffer}(s) or {spaceship}(s) under consideration.baitAn object in a {converter}, usually a small {still life}, that is temporarily destroyed by an incoming {signal}, but in such a way that a usable output signal is produced. In general such a converter produces multiple output signals (or a signal {splitter} is added) and one branch of the output is routed to a {factory} mechanism that rebuilds the bait object so that the converter can be re-used.bakerA {fuse} by Keith McClelland. c p4 fuse            baker's dozenA {loaf} {hassle}d by two {block}s and two {caterer}s. The original form (using p4 and p6 oscillators to do the hassling) was found by Robert Wainwright in August 1989.p12-                   bakery$A common formation of two bi-loaves.p1    banana sparkA common three-bit {polyplet} spark used in {glider synthesis} and {signal} {circuit}ry. The {buckaroo} is an {oscillator} that produces this spark. It can be used to turn a glider 90 degrees: barberpoleYAny p2 oscillator in the infinite sequence {bipole}, {tripole}, {quadpole}, {pentapole}, {hexapole}, {heptapole} ... (It wasn't my idea to suddenly change from Latin to Greek.) This sequence of oscillators was found by the MIT group in 1970. The term is also used (usually in the form "barber pole") to describe other {extensible} sections of oscillators or spaceships, especially those (usually of period 2) in which all generations look alike except for a translation and/or rotation/reflection. Any barberpole can be lengthened by the reaction shown in {barbershop}. See also {pseudo-barberpole}.barberpole intersection= {quad} barbershopAn object created by Jason Summers in 1999 which builds an infinite {barberpole}. It uses {slide gun}s to repeatedly lengthen a {barberpole} at a speed of c/124. The key lengthening reaction from Mark Niemiec is shown below:          barber's pole= {barberpole}bargep1 basic shuttle= {queen bee shuttle}beaconAThe third most common {oscillator}. Found by Conway, March 1970.p2 beacon maker c p8 fuse           beehive$The second most common {still life}.p1beehive and dockp1beehive on big table= {beehive and dock}beehive pusher= {hivenudger}beehive stopper'A {Spartan} logic circuit discovered by Tanner Jacobi on 12 May 2015. It converts an input {glider} {signal} into a {beehive}, in such a way that the beehive can cleanly absorb a single glider from a perpendicular glider {stream}. The circuit can't be re-used until the beehive "bit" is cleared by the passage of at least one perpendicular input. This term has sometimes been used for the beehive {catalyst} variant of {SW-2}, and also for Paul Callahan's larger {glider stopper}, which also provides optional 0-degree and 180-degree glider outputs.1                  beehive wireSee {lightspeed wire}.beehive with tailp1 BellmanlA program for searching catalytic reactions, developed by Mike Playle, which successfully found the {Snark}. belly spark<The spark of a {MWSS} or {HWSS} other than the {tail spark}.Beluchenko's p37Found by Nicolay Beluchenko on April 14, 2009. It was the first {period} 37 {oscillator} to be found, and remains the smallest.p37|         # $  # $       #$#$     # ### $ $$$%%Beluchenko's p51wFound by Nicolay Beluchenko on February 17, 2009. It was the first non-{trivial} {period} 51 {oscillator} to be found.p51p ! !              $$$$       ! !    !!!!$$$$%% bent keysLFound by Dean Hickerson, August 1989. See also {odd keys} and {short keys}.p3     BFx59HOne of the earliest and most remarkable {converter}s, discovered by Dave Buckingham in July 1996. In 59 generations it transforms a B-heptomino into a clean Herschel with very good clearance, allowing easy connections to other conduits. It forms the final stage of many of the known {composite conduit}s, including the majority of the original sixteen {Herschel conduit}s. Here a {ghost Herschel} marks the output location:                B-heptominoUThis is a very common {methuselah} that evolves into three {block}s, two {glider}s and a {ship} after 148 generations. Compare with {Herschel}, which appears at generation 20 of the B-heptomino's evolution. B-heptominoes acquired particular importance in 1996 due to Dave Buckingham's work on {B track}s. See in particular {My Experience with B-heptominos in Oscillators}. This pattern often arises with the cell at top left shifted one space to the left, producing a seven-bit {polyplet} that shares the same eight-bit descendant but is not technically a heptomino at all. This alternate form is shown as the input for {elementary} {converter} patterns such as {BFx59H} and {BRx46B}. This is standard practice for elementary {conduit}s, since many of these conduits do in fact produce this alternate form as output. The B-heptomino is considered a failed {puffer} or failed {spaceship}, since on its own it travels at c/2 for only a short time before being affected by its own trailing debris. However, it can be stabilized into a c/2 puffer or into a {clean} c/2 rake or spaceship. See, e.g., {ecologist}.stabilizes at time 148B-heptomino shuttle= {twin bees shuttle}bi-block!The smallest {pseudo still life}.p1 bi-block fuseA {clean} {fuse} made by a row of {bi-block}s separated by 2 cell gaps. The bi-block row {wick} is usually created by a {bi-block puffer}. The {burn}ing advances 8 cells every 12 generations making its speed {2c/3}.^  !$%(),-    !$%()+.,-    !$%()    !$%()/bi-block pufferAny {puffer} whose output is {bi-block}s. The term is particularly used for p8 c/2 puffers, in which case a {bi-block fuse} is created. A bi-block puffer is easily made using two {backrake}s whose gliders impact symmetrically. Jason Summers {weld}ed two backrakes to form a more compact puffer, as shown below. By periodically burning the {bi-block fuse} using perturbations by a following backrake and spaceships, c/2 rakes can be created for all periods that are a multiple of eight.                                        % ( ) , - 0 1 4 5 8 9    $ % ( ) , - 0 1 4 5 8 9      $%(),-014589 %(),-014589                         :bi-boat = {boat-tie}biclockAThe following {pure glider generator} consisting of two {clock}s.  big beacon = {figure-8}big fish= {HWSS} big gliderwThis was found by Dean Hickerson in December 1989 and was the first known diagonal {spaceship} other than the {glider}.c/4 diagonallyp4D                                    big Sp1 big table= {dock}billiard table!= {billiard table configuration}.billiard table configurationAny {oscillator} in which the {rotor} is enclosed within the {stator}. Examples include {airforce}, {cauldron}, {clock II}, {Hertz oscillator}, {negentropy}, {pinwheel}, {pressure cooker} and {scrubber}.bi-loafThis term has been used in at least three different senses. A bi-loaf can be half a {bakery}: or it can be the following much less common {still life}: or the following {pure glider generator}:bipoleThe {barberpole} of length 2.p2bi-pondp1bi-ship = {ship-tie}bistable switchA {Spartan} {memory cell} found by Paul Callahan in 1994. It can be in one of two states, containing either a {boat} or a {block}. Input gliders on the appropriate paths can change the boat to a block, or vice-versa, while also emitting an output glider. Unlike many memory cells, attempts to change the state to the one it is already in are ignored with the glider passing through with no reaction. This makes it easy to reset the memory cell to a known state. Which of the two states is considered the SET and which considered the RESET is just a matter of convention. The pattern below shows the "boat" state of the memory cell in its original 1994 form. Two gliders are also shown to indicate the input paths used to change the states. A smaller version is shown under {century eater}, with the circuit in its "block" state. As shown, the rightmost glider changes the state from a boat to a block and emits a glider to the upper right, while the leftmost glider passes through unchanged. Alternatively, when the state contains a block, then the leftmost glider changes the state from a block to a boat, and emits a glider to the lower right, while the rightmost glider passes through unchanged.5 !"#"#./.,.,-% $&$&%+78,78*+,+!*","+#,#, ,- -.//90bit A live {cell}, if used in reference to {still life} {population}. For example, a {beehive} is a 6-bit still life. Other uses generally involve information storage: a {memory cell} such as a {honey bit} that can hold one binary bit of information for later retrieval."biting off more than they can chew"Found by Peter Raynham, July 1972.p3  Black&White= {Immigration} blasting caplThe {pi-heptomino} (after the shape at generation 1). A term used at MIT and still occasionally encountered.blinkerHThe smallest and most common {oscillator}. Found by Conway, March 1970.p2 blinker fuseA {clean} {fuse} made from a row of blinkers separated by one cell gaps. The blinker row {wick} is usually created by a {blinker puffer}. The fuse can {burn} in at least three different ways at a speed of {2c/3} depending on the method used to ignite the end of the row of blinkers. This variant has found the most use. The burning advances 12 cells every 18 generations. Fuses can also be made with blinker rows which contain occasional two cell gaps, since the burning reaction is able to bridge those gaps.<4-.035,.01235     !"$%&()*,,.01235-.03546blinker puffer+Any {puffer} whose output is {blinker}s. However, the term is particularly used for p8 c/2 puffers. The first such blinker puffer was found by Robert Wainwright in 1984, and was unexpectedly simple: Since then many more blinker puffers have been found. The following one was found by David Bell in 1992 when he was trying to extend an {x66}: The importance of this larger blinker puffer (and others like it), is that the engine which produces the blinker output is only p4. The blinker row produced by the puffer can easily be ignited, and the resulting {blinker fuse} burns cleanly with a speed of 2c/3. When the burning catches up to the engine, it causes a {phase change} in the puffer. This fact allows p8 blinker puffers to be used to construct rakes of all periods which are large multiples of four.%               blinker pull^The following glider/blinker collision, which moves a blinker (-1,3) toward the glider source:blinkers bit pole&Found by Robert Wainwright, June 1977.p2 blinker ship[A {growing spaceship} in which the wick consists of a line of {blinker}s. An example by Paul Schick based on his {Schick engine} is shown below. Here the front part is p12 and moves at c/2, while the back part is p26 and moves at 6c/13. Every 156 generations 13 blinkers are created and 12 are destroyed, so the wick becomes one blinker longer.?                       block#The most common {still life}, and also the most common object produced by {2-glider collision}s (six different ways). This can be used as a {catalyst} in many reactions. For examples, it can destroy the {beehive} produced by the {queen bee shuttle} and can destroy an evolving {honey farm}:p1blockadeFA common formation of four blocks. The final form of {lumps of muck}.p1   block and dockp1block and gliderstabilizes at time 106blocker/Found by Robert Wainwright. See also {filter}.p8    block factoryAny {factory} {circuit} that produces a {block} in response to an input signal. For a useful high-{clearance} example see {keeper}.BlockicAdjective for {constellation}s consisting entirely of {block}s. It's possible to arrange blocks in a way that can be {trigger}ed by a single glider to produce any {glider constructible} pattern. A simple example of a Blockic pattern is shown under {fuse}. See also {seed}. block keeper See {keeper}.block-laying switch engineSee {stabilized switch engine}.block on big table= {block and dock}block on tablep1  block pullThe following glider/block collision, which moves a block (2,1) toward the glider source. Performing this reaction twice using a {salvo} of two gliders can move a block diagonally back by three cells, which can be of use for a {sliding block memory}.  block pusherA pattern emitting streams of {glider}s which can repeatedly push a block further away. This can be used as part of a {sliding block memory}. The following pattern, in which three gliders push a block one cell diagonally, is an example of how a block pusher works. A universal {construction elbow} recipe library is also likely to contain one or more block-pushing reactions, since blocks are commonly used as elbows.   blomAThe following {methuselah}, found by Dean Hickerson in July 2002.stabilizes at time 23314      blonkA {block} or a {blinker}. This term is mainly used in the context of {sparse Life} and was coined by Rich Schroeppel in September 1992.blonkerFThe following {oscillator}, found by Nicolay Beluchenko in April 2004.p6       BLSE= {block-laying switch engine}BNE14T30OA {B-heptomino} to {glider} {converter} found by Tanner Jacobi on 26 May 2016. This converter has the unusual property of being an {edge shooter} where no part of the reaction's {envelope} extends beyond the glider's output {lane}. It can be easily connected to {Herschel circuit}ry via {HFx58B} or other known {elementary} conduits."             boatTThe only 5-cell {still life}. A boat can be used as a 90-degree {one-time} {turner}.p1boat-bitA binary digit represented by the presence of a {boat} next to a {snake} (or other suitable object, such as an {aircraft carrier}). The bit can be toggled by a {glider} travelling along a certain path. A correctly timed glider on a crossing path can detect whether the transition was from 1 to 0 (in which case the crossing glider is deleted) or from 0 to 1 (in which case it passes unharmed). Three gliders therefore suffice for a {non-destructive read}. The mechanisms involved are shown in the diagram below. Here the bit is shown in state 0. It is about to be set to 1 and then switched back to 0 again. The first crossing glider will survive, but the second will be destroyed. In January 1997 David Bell found a method of reading the bit while setting it to 0. A {MWSS} is fired at the boat-bit. If it is already 0 (absent) then the MWSS passes unharmed, but if it is 1 (present) then the boat and the MWSS are destroyed and, with the help of an {eater1}, converted into a glider which travels back along exactly the same path that is used by the gliders that toggle the boat-bit. There are many other equivalent methods based on alternate incoming test {signal}s.      boat maker c p4 fuse              boat on boat = {boat-tie} boat-ship-tie= {ship tie boat} boatstretcherSee {tubstretcher}.boat-tiedA 10-cell {still life} consisting of two {boat}s placed tip-to-tip. The name is a pun on "bow tie".p1 bobsled= {switch engine channel}.boojum reflectorFDave Greene's name for the following 180-degree {glider} {reflector} which he found in April 2001, winning $100 bounties offered by Alan Hensel and Dieter Leithner. The name is taken from Lewis Carroll's _The Hunting of the Snark_, referring to the fact that a small 90-degree stable reflector was really what was wanted. 180-degree reflectors are relatively undesirable and have limited use in larger circuitry constructions. The boojum reflector was the smallest and fastest known stable reflector until the discovery of the {rectifier} in 2009, followed by the {Snark} in 2013.p1A  ( ' ) ' )   & ' ) *   &')*&')+*+"#"#()  (*  * *+  "#"#, bookendAThe following {induction coil}. It is generation 1 of {century}.bookendsp1bossFound by Dave Buckingham, 1972.p4*                bottleaFound by Achim Flammenkamp in August 1994. The name is a back-formation from {ship in a bottle}.p8P                             bouncerA label used for the small periodic {colour-changing} {glider} {reflector}s discovered mainly by Noam Elkies in the late 1990s. See {p5 bouncer}, {p6 bouncer}, {p7 bouncer}, {p8 bouncer}, or {p15 bouncer}. bounding boxlThe smallest rectangular array of cells that contains the whole of a given pattern. For {oscillator}s and {gun}s this usually is meant to include all {phase}s of the pattern, but in the case of guns, the outgoing stream(s) are excluded. The bounding box is one of the standard ways to measure the size of an object; the other standard metric is the {population}.bow tie = {boat-tie}brainFound by David Bell, May 1992.c/3 orthogonallyp3F                            branching spaceship[An {extensible} spaceship containing {component}s which can be attached in multiple ways so that the result can contain arbitrarily many {arm}s arranged like a binary tree. Here is an example of a period 2 c/2 branching spaceship, which also includes a {wicktrailer}: Branching spaceships have also been constructed for other speeds, such as c/3.'&'(%&')*#$&) "$)+,"$')+,!"#,123#$,-04/45     , - . / 2 3 5      . 0 5 6       4         6 7 8      8 9 99:  %&' !$(#()    !"#&')  "$)* (  *+, ,- --..+,-.345*+./26 # $ % * 1 6 7 !!!!"!&!)!*!.!/!0!1!4!5!7!""""!"""'"0"2"7"8"#!###$#'#(#)#*#6#$$ $!$&$($8$9$:$%"%:%;%&&&&&& &;& '''''';'<'((<())))9):);)<)**8*9*<*=*++++++++8+,,,,,,, ,7,8,- -7-.. .!.7.8.9.:./6/7/:/;/0000;0 1111;1<1233>4breeder/Any pattern whose {population} grows at a quadratic rate, although it is usual to exclude {spacefiller}s. It is easy to see that this is the fastest possible growth rate. The term is also sometimes used to mean specifically the breeder created by Bill Gosper's group at MIT, which was the first known pattern exhibiting {superlinear growth}. There are four common types of breeder, known as MMM, MMS, MSM and SMM (where M=moving and S=stationary). Typically an MMM breeder is a {rake} {puffer}, an MMS breeder is a puffer producing puffers which produce stationary objects ({still life}s and/or {oscillator}s), an MSM breeder is a {gun} puffer and an SMM breeder is a rake gun. There are, however, less obvious variants of these types. Other less common breeder categories (SSS, hybrid MSS/MSM, etc.) can be created with some difficulty, based on {universal constructor} technology; see {Pianola breeder}. The original breeder was of type MSM (a p64 puffer puffing p30 glider guns). The known breeder with the smallest initial population is {switch-engine ping-pong}.bridgeA term used in naming certain {still life}s (and the {stator} part of certain {oscillator}s). It indicates that the object consists of two smaller objects joined edge to edge, as in {snake bridge snake}. broken linesnA pattern constructed by Dean Hickerson in May 2005 which produces complex broken lines of gliders and blocks.broth= {soup}BRx46BA {Spartan} {elementary conduit} discovered by Michael Simkin on 25 April 2016, one of the relatively few known conduits that can move a {B-heptomino} input to a B-heptomino output without an intervening {Herschel} stage.          BTC = {billiard table configuration}B track>A {track} for {B-heptomino}es. A B-heptomino becomes a {Herschel} plus a {block} in twenty generations, so this term was nearly synonymous with {Herschel track} until the discovery of {elementary conduit}s that convert a B directly to another B, or to some other non-Herschel signal output. See for example {BRx46B}.BTS>A 19-cell {still life} made up of a {bookend}, a {table}, and a {snake}. Starting in 2015, with the help of Mike Playle's {Bellman} search program, Tanner Jacobi discovered a surprising number of ways to use this object as a {catalyst} for {signal} {circuit}ry. One example can be seen in the {CC semi-cenark} entry.buckarooA {queen bee shuttle} stabilized at one end by an eater in such a way that it can turn a glider, as shown below. The glider turning reaction uses a {banana spark} and is {colour-preserving}. The mechanism was found by Dave Buckingham in the 1970s. The name is due to Bill Gosper.p30              bullet heptomino"Generation 1 of the {T-tetromino}.bumperOne of several periodic {colour-preserving} {glider} {reflector}s discovered by Tanner Jacobi on 6 April 2016. See {p3 bumper}, {p4 bumper}, {p5 bumper}, {p6 bumper}, {p7 bumper}, {p8 bumper}, {p9 bumper}, {p11 bumper}, and {p15 bumper}.bun~The following {induction coil}. By itself this is a common {predecessor} of the {honey farm}. See also {cis-mirrored R-bee}.bunniesfThis is a {parent} of {rabbits} and was found independently by Robert Wainwright and Andrew Trevorrow.stabilizes at time 17332 burloaf= {loaf}burloaferimeter7Found by Dave Buckingham in 1972. See also {airforce}.p7     burn|A reaction which travels indefinitely as a {wave} through the components of a {wick} or an {agar}. A burning wick is known as a {fuse}. If the object being burned has a spatial periodicity, then the active area of the burning usually remains bounded and so eventually develops a periodicity too. It is unknown whether this will always occur. The speed of burning can range from arbitrarily slow up to the {speed of light}. The results of burning can be clean (leaving no debris), or leaving debris usually much different from the original object. In rare cases, a {reburnable fuse} produces an exact copy of the original object, allowing the creation of objects such as the {telegraph}. In many useful cases burning can be initiated by impacting an object with {glider}s or other {spaceship}s. An object might be able to burn in more than one way, depending on how the burn is initiated.bushingaThat part of the {stator} of an {oscillator} which is adjacent to the {rotor}. Compare {casing}. butterflyThe following pattern, or the formation of two beehives that it evolves into after 33 generations. (Compare {teardrop}, where the beehives are five cells closer together.)Bx125JAn {elementary conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in November 1998. After 125 ticks, it produces an inverted {Herschel} rotated 180 degrees at (-9, -17) relative to the input. Its {recovery time} is 166 ticks. A {ghost Herschel} in the pattern below marks the output location:/    $%$%       &Bx222A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in October 1998. It is made up of three {elementary conduit}s, HF95P + PB68B + {BFx59H}. After 222 ticks, it produces a mirror-reflected {Herschel} rotated 180 degrees, at (6, -16) relative to the input. Its {recovery time} is 271 ticks. A {ghost Herschel} in the pattern below marks the output location:Z         %$&$&#$&'()    # $ & ' (    # $ &   ()(&(&'      !!"##*$by flopsFound by Robert Wainwright.p2 c= {speed of light}c/10 spaceshipA {spaceship} travelling at one tenth of the {speed of light}. The first such spaceship to be discovered was the orthogonally travelling {copperhead}, found by 'zdr' on 5 March 2016. Simon Ekstrom found the related {fireship} two weeks later. A {Caterloopillar} can theoretically be configured to move at c/10, but there are technical difficulties with speeds of the form 4n+2, and as of June 2018 this has not been done in practice.c/12 spaceshipA {spaceship} travelling at one twelfth of the {speed of light}. The only diagonal spaceships that are currently known to move at this speed are the {Cordership}s. An orthogonal {Caterloopillar} has been configured to move at c/12. c/2 spaceshipgA {spaceship} travelling at half the {speed of light}. Such spaceships necessarily move orthogonally. The first to be discovered was the {LWSS}. For other examples see {Coe ship}, {ecologist}, {flotilla}, {hammerhead}, {hivenudger}, {HWSS}, {MWSS}, {puffer train}, {puff suppressor}, {pushalong}, {Schick engine}, {sidecar}, {still life tagalong} and {x66}. c/3 spaceshipA {spaceship} travelling at one third of the {speed of light}. All known c/3 spaceships travel orthogonally. The first was {25P3H1V0.1}, found in August 1989 by Dean Hickerson. For further examples see {brain}, {dart}, {edge-repair spaceship}, {fly}, {turtle} and {wasp}. c/4 spaceshipMA {spaceship} travelling at one quarter of the {speed of light}. The first such spaceship to be discovered was, of course, the {glider}, and this remained the only known example until December 1989, when Dean Hickerson found the first orthogonal example, {119P4H1V0}, and also a new diagonal example (the {big glider}). For other examples see {B29}, {Canada goose}, {crane}, {Enterprise}, {edge-repair spaceship} (third pattern), {non-monotonic}, {Orion}, {quarter}, {sparky}, {swan} and {tagalong}. It is known that c/4 is the fastest possible speed for a (45-degree) diagonal spaceship. c/5 spaceshipA {spaceship} travelling at one fifth of the {speed of light}. The first such spaceship to be discovered was the {snail}, found by Tim Coe in January 1996. The first diagonally moving example, {295P5H1V1}, was found by Jason Summers in November 2000. For other c/5 ships see {58P5H1V1}, {67P5H1V1}, {86P5H1V1} and {spider}. A {Caterloopillar} has also been configured to move at c/5. c/6 spaceshipLA {spaceship} travelling at one sixth of the {speed of light}. The first such spaceship to be discovered was the {dragon}, found by Paul Tooke in April 2000. The first diagonally moving example was the {seal}, found by Nicolay Beluchenko in September 2005. Another orthogonal c/6 spaceship, found by Paul Tooke in March 2006, is shown below. For the smallest known c/6 spaceship see {56P6H1V0}. A {Caterloopillar} can theoretically be configured to move at c/6, but there are technical difficulties with speeds of the form 4n+2, and as of July 2018 this has not been done in practice.4%&235 &.2!#%&'-/16  !"#$%(+/36!$%(*,-0   "$'*,.569   !"$&'-5679  !"$%&*+,-79         ! " $ % & * + , - 7 9       ! " $ & ' - 5 6 7 9        " $ ' * , . 5 6 9            ! $ % ( * , - 0   !"#$%(+/36!#%&'-/16 &.2%&2354: c/7 spaceship^A {spaceship} travelling at one seventh of the {speed of light}. The first such spaceship to be discovered was the diagonally travelling {lobster}, found by Matthias Merzenich in August 2011. The first known orthogonal c/7 spaceship was the {loafer}, discovered by Josh Ball in February 2013. A {Caterloopillar} has been configured to move at c/7.CA= {cellular automaton} caber tosseryAny pattern whose {population} is asymptotic to c.log(t) for some constant c, and which contains a {glider} (or other {spaceship}) bouncing between a slower receding spaceship and a fixed {reflector} which emits a spaceship (in addition to the reflected one) whenever the bouncing spaceship hits it. As the receding spaceship gets further away the bouncing spaceship takes longer to complete each cycle, and so the extra spaceships emitted by the reflector are produced at increasingly large intervals. More precisely, if v is the speed of the bouncing spaceship and u the speed of the receding spaceship, then each interval is (v+u)/(v-u) times as long as the previous one. The population at time t is therefore n.log(t)/log((v+u)/(v-u)) + O(1), where n is the population of one of the extra spaceships (assumed constant). The first caber tosser was built by Dean Hickerson in May 1991.Callahan G-to-HA stable {glider reflector} and glider-to-Herschel {converter} discovered by Paul Callahan in November 1998. Its recovery time is 575 ticks. The initial stage converts two gliders into a Herschel. A {ghost Herschel} in the pattern below marks the output location: The glider from the southeast can be supplied by an {Fx77} + {L112} + Fx77 Herschel track, or by reflecting the output Herschel's {FNG} as in the {p8 G-to-H}. See also {Silver reflector}, {Silver G-to-H}.<              !     !            "Cambridge pulsar CP 48-56-72= {pulsar} (The numbers refer to the populations of the three {phase}s. The Life pulsar was indeed discovered at Cambridge, like the first real pulsar a few years earlier.) Canada goose>Found by Jason Summers, January 1999. It consists of a {glider} plus a {tagalong}. At the time of its discovery the Canada goose was the smallest known diagonal {spaceship} other than the glider, but this record has since been beaten, first by the second spaceship shown under {Orion}, and more recently by {quarter}.c/4 diagonallyp4$               candelabra3By Charles Trawick. See also the note under {cap}.p3          candlefrobraFound by Robert Wainwright in November 1984. The following diagram shows that a pair of these can act in some ways like {killer toads}. See also {snacker}.p3   canoep1capThe following {induction coil}. It can also easily be stabilized to form a p3 oscillator. See {candelabra} for a slight variation on this.carnival shuttlevFound by Robert Wainwright in September 1984 (using {MW emulator}s at the end, instead of the {monogram}s shown here).p12:!%!"#$%  #  "$  #!"#$%!%&carrier= {aircraft carrier}casingfThat part of the {stator} of an {oscillator} which is not adjacent to the {rotor}. Compare {bushing}. catacrystA 58-cell {quadratic growth} pattern found by Nick Gotts in April 2000. This was formerly the smallest such pattern known, but has since been superseded by the related {metacatacryst}. See {switch-engine ping-pong} for the lowest-population {superlinear growth} pattern as of July 2018, along with a list of the record-holders. The catacryst consists of three {ark}s plus a glider-producing {switch engine}. It produces a block-laying switch engine every 47616 generations. Each block-laying switch engine has only a finite life, but the length of this life increases linearly with each new switch engine, so that the pattern overall grows quadratically, as an unusual type of MMS {breeder}. CatagolueAn online database of objects in Conway's Game of Life and similar cellular automata, set up by Adam P. Goucher in 2015 at {http://catagolue.appspot.com}. It gathers data from a distributed search of random initial configurations and records the eventual decay products. Within a year of operation it had completed a {census} of the {ash} objects from over two trillion asymmetric 16x16 {soup}s. As of June 2018, well over two hundred trillion ash objects have been counted, from over a trillion asymmetric soups. It is often possible to use Catagolue search results find equivalent {glider synthesis} recipes for selected parts of long-running active reactions. These random {soup} searches have made it possible to find efficient construction methods for thousands of increasingly rare {still life}s and {oscillator}s, and the occasional {puffer} or {spaceship}. In many of these cases a {glider synthesis} was previously very difficult or unknown.catalyst&An object that participates in a reaction but emerges from it unharmed. All {eater}s are catalysts. Some small {still life}s can act as catalysts in some situations, such as the {block}, {ship}, and {tub}. The still lifes and oscillators that form a {conduit} are examples of catalysts. A relatively rare form of catalysis occurs in a {transparent debris effect}, where the catalyst in question is completely destroyed and then rebuilt. The term is also sometimes used for a modification of an active reaction in a {rake} by passing {spaceship}s.catch and throwA {technology} used (e.g., in the {Caterpillar}) to adjust the timing of a glider by turning it into a stationary object using one interaction, and then later restoring it using a second interaction. The interactions are caused by passing objects which are not otherwise affected. The direction of the glider is not usually changed. Here is an example where a glider is turned into a {boat} by the first {LWSS}, and is then restored by the remaining {spaceship}s:E"#12:;<= %013456:>123456:%2345;> !"#$       !"# !"# !"?caterer(Found by Dean Hickerson, August 1989. Compare with {jam}. In terms of its minimum {population} of 12 this is the smallest p3 {oscillator}. See also {double caterer} and {triple caterer}. More generally, any oscillator which serves up a {bit} in the same manner may be referred to as a caterer.p3 CaterloopillarA family of adjustable-speed {spaceship}s constructed by Michael Simkin in 2016, based on an "engineless caterpillar" idea originally proposed by David Bell. The front and back halves of Caterloopillars each function as universal constructors, with each half constructing the building blocks of the other half, while also reading and moving a construction tape. The overall design is reminiscent of M.C. Escher's lithograph "Drawing Hands". The name "Caterloopillar" is a reference to Douglas Hofstader's Strange Loop concept. Simkin has written an automated script that can construct a Caterloopillar for any rational speed strictly less than c/4, with some exceptions. Speeds closer to the c/4 limit in general require larger constructions, and for any given computer system it is easy to choose a speed that makes it impractical to construct a Caterloopillar. As of June 2018 one significant remaining exception is that Caterloopillars with periods c/(6+4N) can't be constructed. This is only a limitation of the current construction script, not of the underlying Caterloopillar {toolkit}. For technical reasons, the lowest speed that the current script can produce is around c/95. The slowest Caterloopillars that have been explicitly constructed to date are c/87 and c/92. These are among the smallest in terms of population, though their bounding boxes are larger than some of the higher-speed Caterloopillars. CaterpillarA {spaceship} that works by laying tracks at its front end. The first example constructed was a p270 17c/45 spaceship built by Gabriel Nivasch in December 2004, based on work by himself, Jason Summers and David Bell. This Caterpillar has a population of about 12 million in each generation and was put together by a computer program that Nivasch wrote. At the time it was by far the largest and most complex Life object ever constructed, and it is still one of the largest in terms of population. The 17c/45 Caterpillar is based on the following reaction between a {pi-heptomino} and a {blinker}: In this reaction, the pi moves forward 17 cells in the course of 45 generations, while the blinker moves back 6 cells and is rephased. This reaction has been known for many years, but it was only in September 2002 that David Bell suggested that it could be used to build a 17c/45 spaceship, based on a reaction he had found in which pi-heptominoes crawling along two rows of blinkers interact to emit a glider every 45 generations. Similar glider-emitting interactions were later found by Gabriel Nivasch and Jason Summers. The basic idea of the spaceship design is that streams of gliders created in this way can be used to construct fleets of {standard spaceship}s which convey gliders to the front of the blinker tracks, where they can be used to build more blinkers. A different Caterpillar may be possible based on the following reaction, in which the pattern at top left reappears after 31 generations displaced by (13,1), having produced a new NW-travelling glider. In this case the tracks would be waves of backward-moving gliders. For other Caterpillar-type constructions see {Centipede}, {waterbear}, {half-baked knightship}, and {Caterloopillar}.  CatForcevAn optimized {search program} written by Michael Simkin in 2015, using brute-force enumeration of small {Spartan} objects in a limited area, instead of a depth-first tree search. One major purpose of CatForce is to find glider-constructible completions for signal conduits. An early CatForce discovery was the {B60} conduit, which enabled a record-breaking new glider gun.Catherine wheel = {pinwheel}cauldronaFound in 1971 independently by Don Woods and Robert Wainwright. Compare with {Hertz oscillator}.p8             cavity= {eater plug}CC semi-cenarkThe {colour-changing} version of Tanner Jacobi's century-based semi-Snark mechanism, using a {C-to-G} consisting of a {BTS} {catalyst} and a {block}. See {CP semi-cenark} for the {colour-preserving} version, or {semi-cenark} for repeat time details and an alternate initial catalyst.H                  CC semi-Snark+A small 90-degree {colour-changing} {glider reflector} requiring two input gliders on the same lane for each output glider. It was discovered by Sergei Petrov on 1 July 2013, using a custom-written search utility. It functions as a very compact {period doubler} in some {signal} {circuit}ry, for example the {linear propagator}. The semi-Snark can period-double a regular glider {stream} of period 51 or more, or an {intermittent stream} with two gliders every 67 ticks or more, since the block reset glider can be sent just 16 ticks before its partner.)              cellThe fundamental unit of space in the Life universe. The term is often used to mean a live cell - the sense is usually clear from the context.cellular automaton-A certain class of mathematical objects of which {Life} is an example. A cellular automaton consists of a number of things. First there is a positive integer n which is the dimension of the cellular automaton. Then there is a finite set of states S, with at least two members. A state for the whole cellular automaton is obtained by assigning an element of S to each point of the n-dimensional lattice Z^n (where Z is the set of all integers). The points of Z^n are usually called cells. The cellular automaton also has the concept of a neighbourhood. The neighbourhood N of the origin is some finite (nonempty) subset of Z^n. The neighbourhood of any other cell is obtained in the obvious way by translating that of the origin. Finally there is a transition rule, which is a function from S^N to S (that is to say, for each possible state of the neighbourhood the transition rule specifies some cell state). The state of the cellular automaton evolves in discrete time, with the state of each cell at time t+1 being determined by the state of its neighbourhood at time t, in accordance with the transition rule. There are some variations on the above definition. It is common to require that there be a quiescent state, that is, a state such that if the whole universe is in that state at generation 0 then it will remain so in generation 1. (In Life the OFF state is quiescent, but the ON state is not.) Other variations allow spaces other than Z^n, neighbourhoods that vary over space and/or time, probabilistic or other non-deterministic transition rules, etc. It is common for the neighbourhood of a cell to be the 3x...x3 (hyper)cube centred on that cell. (This includes those cases where the neighbourhood might more naturally be thought of as a proper subset of this cube.) This is known as the Moore neighbourhood.census0A count of the number of different individual Life objects within one larger object, most often the final {ash} of a random {soup} experiment. This includes the number of {block}s, {blinker}s, {glider}s, and other common objects, as well as any rarer larger {still life}s, {oscillator}s or {spaceship}s.centinal|Found by Bill Gosper. This combines the mechanisms of the p46 and p54 shuttles (see {twin bees shuttle} and {p54 shuttle}).p100F23202 '(01  ')  )  '()   ' ( ) ) ' )     ' ( 0 1 022234 CentipedexThe smallest known {31c/240} spaceship, constructed by Chris Cain in September 2014 as a refinement of the {shield bug}.31c/240 orthogonallyp240centuryThis is a common pattern which evolves into three {block}s and a {blinker}. In June 1996 Dave Buckingham built a neat {p246 gun} using a century as the engine. See also {bookend} and {diuresis}.stabilizes at time 103 century eater5A 20-cell {still life} that functions as an {eater} for the active reaction produced by any {century} relative. The most well-known use is to replace a four-object {constellation} in Paul Callahan's {bistable switch}, as shown below. In September 2014 Josh Ball showed that a variant of this still life has a relatively inexpensive {slow glider construction} {recipe}. At T=256 the active reaction produces an eight-cell pattern sharing the same grandchild as a century. The century eater at the top of the pattern catalyzes this pattern produce a clean {spark}.(           &&''()) ) ) * *+century-to-glider converter+Any {signal} {circuit} that accepts a {century} as input and produces a clean output {glider}. For example, in November 2017 Adam P. Goucher noticed that this previously known C-to-G {converter} can replace the {century eater} in Paul Callahan's {bistable switch}, producing an extra glider output.   channelA {lane} or {signal} path used in construction circuitry. Until the invention of {single-channel} {construction arm}s, signals in a channel would usually be {synchronized} with one or more coordinated signals on other paths, as in the {Gemini}, which used twelve channels to run three construction arms simultaneously, or the 10hd {Demonoid} which needed only two channels. See also {Geminoid}.chaotic growthAn object whose {fate} is unknown, except that it appears to grow forever in an unpredictable manner. In Life, no pattern has yet been found that is chaotic. This is in contrast to many other Life-like rules, where even small objects can appear to grow chaotically. It is possible that chaotic growth may occur rarely or even regularly for large enough random Life objects, but if so the minimum size of such patterns must be larger than what can currently be experimentally simulated (but see {novelty generator}). In any case, it is not decidable whether a pattern that apparently grows randomly forever is in fact displaying chaotic growth. Continuing to evolve such a pattern might at any time result in it suddenly cleaning itself up and becoming predictable.chemistp50                        C-heptomino^Name given by Conway to the following {heptomino}, a less common variant of the {B-heptomino}. Cheshire catA block {predecessor} by C. R. Tompkins that unaccountably appeared both in Scientific American and in {Winning Ways}. See also {grin}. chicken wireA type of {stable} {agar} of {density} 1/2. The simplest version is formed from the tile: But the "wires" can have length greater than two and need not all be the same. For example: chirality A term borrowed from chemistry to describe asymmetrical patterns with two distinct mirror-image orientations. One common use is in relation to {Herschel transmitter}s, where the spacing between the two gliders in the {tandem glider} output can limit the {receiver} to a single chirality.cigar = {mango}circuit/Any combination of {conduit}s or {converter}s that moves or processes an active {signal}. This includes components with multiple states such as {period multiplier}s or {switch}es, which can be used to build {gun}s, logic gates, {universal constructor}s, and other computation or construction circuitry.cis-beacon on anvilp2 cis-beacon on tablep2 cis-boat with tailp1 cis fuse with two tailsSee also {pulsar quadrant}.p1 cis-mirrored R-beep1 cis snake = {canoe}cleanOpposite of {dirty}. A reaction which produces a small number of different products which are desired or which are easily deleted is said to be clean. For example, a {puffer} which produces just one object per period is clean. Clean reactions are useful because they can be used as building blocks in larger constructions. When a {fuse} is said to be clean, or to {burn} cleanly, this usually means that no debris at all is left behind. clearance0In signal circuitry, the distance from an {edge shooter} output {lane} to the last unobstructed lane adjacent to the edge-shooter circuitry. For example, an {Fx119 inserter} has an unusually high 27{hd} clearance. Also, oscillator and eater variants may be said to have better clearance if they allow {glider}s or other {signal}s to pass closer to them than the standard variant allows. The following high-clearance {eater1} variant by Karel Suhajda allows gliders to pass one lane closer on the southeast side, than is allowed by the standard fishhook shape. This is considered to be a variant of the eater1 because the reaction's {rotor} is exactly the same, even though three cells in this variant are too overpopulated to allow a birth, instead of underpopulated as in a standard eater1 glider-eating reaction.    clockFound by Simon Norton, May 1970. This is the fifth or sixth most common {oscillator}, being about as frequent as the {pentadecathlon}, but much less frequent than the {blinker}, {toad}, {beacon} or {pulsar}. It is surprisingly rare considering its small size. The protruding cells at the edges can perturb some reactions by inhibiting the birth of a cell in a 3-cell corner. For example, a clock can be used to suppress the surplus {blinker} produced by an {F171} conduit, significantly improving the {recovery time} of the circuit:p2clock IICompare with {pinwheel}.p4#        clock inserter= {clock insertion}.clock insertionA uniquely effective method of adding a glider to the front edge of a {salvo}, by first constructing a {clock}, then converting it to a glider using a one-bit {spark}. Here it rebuilds a sabotaged glider in a deep pocket between other gliders: In 2015 Chris Cain used this reaction to demonstrate conclusively that any unidirectional glider {salvo}, no matter how large or tightly packed, can be constructed by collisions between gliders that are initially separated by any finite distance. As a corollary, because all glider syntheses are made up of two to four unidirectional salvos, any glider-constructible object has a synthesis that starts with every glider at least N cells away from every other glider (for any chosen N).V22423/6.5./0567+2+-24:+ , 2 3 8 9 ( 0 9 : ' ' ( ) 5 7 5 6 631223 ! %!&!""%"'"##%#$-6.6-7/7-8;9cloud of smoke = {smoke} cloverleafThis name was given by Robert Wainwright to his p2 oscillator {washing machine}. But Achim Flammenkamp also gave this name to {Achim's p4}.clusterAny pattern in which each live cell is connected to every other live cell by a path that does not pass through two consecutive dead cells. This sense is due to Nick Gotts, but the term has also been used in other senses, often imprecise.CNWH%Conweh, creator of the Life universe.Coe ship6A {puffer engine} discovered by Tim Coe in October 1995. In December 2015, the Coe ship was discovered in an asymmetric random {soup} on {Catagolue}. This was the first time any non-p4 ship was discovered in a random asymmetric soup experiment, winning Adam P. Goucher a 50-euro prize offered by Ivan Fomichev.c/2 orthogonallyp16     Coe's p8 Found by Tim Coe in August 1997.p8     Collatz 5N+1 simulatorAn {unknown fate} pattern constructed by David Bell in December 2017 that simulates the Collatz 5N+1 algorithm using {sliding block memory} and {p1} {technology}, while always having a population below 32000. The algorithm is simple. Starting with a number, if it is even divide it by 2, otherwise multiply it by 5 and add 1. When this process is iterated a sequence of numbers is generated. When starting with the value of 7, it is currently unknown whether or not the sequence ever forms a cycle. Because of this the fate of the simulator is also currently unknown. It may become stable, or become an oscillator with a high period, or have a bounding box which grows irregularly.colour= {colour of a glider}colour-changingSee {colour of a glider}. The {reflector} shown in {p8 bouncer} is colour-changing, as are its 5/6/7/8 and higher-period versions.colour-changing semi-Snark= {CC semi-Snark}.colourised Life6A {cellular automaton} that is the same as Life except for the use of a number of different ON states ("colours"). All ON states behave the same for the purpose of applying the Life rule, but additional rules are used to specify the colour of the resulting ON cells. Examples are {Immigration} and {QuadLife}.colour of a gliderThe colour of a {glider} is a property of the glider that remains constant while the glider is moving along a straight path, but that can be changed when the glider bounces off a {reflector}. It is an important consideration when building something using reflectors. The colour of a glider can be defined as follows. First choose some cell to be the origin. This cell is then considered to be white, and all other cells to be black or white in a checkerboard pattern. (So the cell with coordinates (m,n) is white if m+n is even, and black otherwise.) Then the colour of a glider is the colour of its leading cell when it is in a phase that can be rotated to look like this: A reflector that does not change the colour of gliders obviously cannot be used to move a glider onto a path of different colour than it started on. But a 90-degree reflector that does change the colour of gliders is similarly limited, as the colour of the resulting glider will depend only on the direction of the glider, no matter how many reflectors are used. For maximum flexibility, therefore, both types of reflector are required. Small periodic colour-changing glider reflectors ({bouncer}s) are known, and also small periodic colour-preserving glider reflectors ({bumper}s). Among stable patterns, only a small colour-preserving reflector ({Snark}) is known. The smallest known 90-degree colour-changing reflector is given at the end of the {reflector} entry.colour-preservingSSee {colour of a glider}. {Snark}s and {bumper}s are colour-preserving reflectors.colour-preserving semi-Snark= {CP semi-Snark}complementary blinker= {fore and back} componentoA partial {glider synthesis} that can be used in the same way in multiple {glider recipe}s. A component transforms part of an object under construction in a well-defined way, without affecting the rest of the object. For example, this well-known component can be used to add a {hook} to any object that includes a protruding {table} end, converting it to a {long bookend}: "Component" is also used to specify any piece of an object - {spaceship}, {oscillator}, etc. - that can be combined with other components in specific ways according to a {grammar} to produce a variety of objects. The components can either be independent objects that only occasionally react with each other, or else they can be fused together to support each other. For example, any {branching spaceship} is made up of several components, and there is a single repeating component in any {wicktrailer}.X/-../*(*)*--/-.       ' ( + .           ' + , - . ()**,+,0 compositeSee {composite conduit}.composite conduit\A signal-processing {conduit} that can be subdivided into two or more {elementary conduit}s. compression!= {repeat time}, {recovery time}.computational universalitySee {universal computer}.conduitAny arrangement of {still life}s and/or {oscillator}s that moves an active object to another location, perhaps also transforming it into a different active object at the same time, but without leaving any permanent debris (except perhaps gliders, or other spaceships) and without any of the still lifes or oscillators being permanently damaged. Probably the most important conduit is the following remarkable one (Dave Buckingham, July 1996) in which a {B-heptomino} is transformed into a {Herschel} in 59 generations. Several hundred {elementary conduit}s are now known, with recent discoveries primarily made via {search program}s such as {CatForce} and {Bellman}.           conduit 1 = {BFx59H}.confused eaters%Found by Dave Buckingham before 1973.p4  constellationA general term for a group of two or more separate objects, usually small still lifes and low-period oscillators. Compare {pseudo still life}.construction arm An adjustable mechanism in a {universal constructor} that allows new objects to be constructed in any chosen location that the arm can reach. A construction arm generally consists of a {shoulder} containing fixed guns or edge shooters, a movable {construction elbow} that slides forward and backward along the {construction lane}(s), and in the case of {single-arm} universal constructors, a {hand} target object at the construction site that can be progressively modified by a {slow salvo} to produce each desired object.construction elbowOne of the components of a {construction arm} in a {universal constructor}. The elbow usually consists of a single {Spartan} still life or small constellation. It accepts {elbow operation} recipes, in the form of {salvo}s coming from the construction arm's {shoulder}. These recipes may do one of several things: 1) {pull} the elbow closer to the shoulder, 2) {push} the elbow farther from the shoulder, 3) emit a glider on a particular output {lane} (while also optionally pushing or pulling the elbow); 4) create a "{hand}" target block or other useful object as a target for output gliders, to one side of the {construction lane}; 5) duplicate the elbow, or 6) destroy the elbow. Elbows that receive and emit orthogonally-travelling {spaceship}s instead of gliders are technically possible, but no working examples are currently known. The discussion below assumes that gliders are used to communicate between the shoulder, elbow, and hand locations. If a mechanism can be programmed to generate recipes for at least the first three options listed above, it is generally capable of functioning as a {universal constructor}. The main requirement is that push and pull {elbow operation}s should be available that are either minimal (1{fd}) or the distances should be relatively prime. Depending on the {elbow operation} library, there may be only one type of elbow, or there may be two or more elbow objects, with recipes that convert between them. The {9hd} library had just one elbow type, a block. The original 10{hd} library had two elbows, blocks in mirror-symmetric locations; this was expanded to a larger list for the {10hd Demonoid}. The {0hd Demonoid} also has a multi-elbow recipe library. A {slow elbow} toolkit may make use of an even larger number of glider output recipes, because the {target} elbow object in that case is not restricted to a single diagonal line. If only one colour, parity, or phase of glider can be emitted, then the mechanism will be limited to producing {monochromatic salvo}s or {monoparity salvo}s. These are less efficient at most construction tasks, but are still generally accepted to enable {universal toolkit}s. See also {half-baked knightship}.construction envelopeThe region affected by an active reaction, such as a {glider synthesis} of an object. The envelope corresponds to the state-2 blue cells in {LifeHistory}. See also {edgy}.construction laneNPart of a {construction arm} between the {shoulder} and the {elbow} - in particular, one of the fixed {lane}s that {elbow operation} signals travel on. All known {universal constructor}s have used arms with two or more construction lanes, except for the ones in the {0hd Demonoid} and in recent {single-channel} construction recipes.construction recipeOne or more streams of {glider}s or other signals fed into a {universal constructor} to create a target object. Compare {glider recipe}.construction universalitySee {universal constructor}. converterA {conduit} in which the input object is not of the same type as the output object. This term tends to be preferred when either the input object or the output object is a {spaceship}. The following diagram shows a p8 {pi-heptomino}-to-{HWSS} converter. This was originally found by Dave Buckingham in a larger form (using a {figure-8} instead of the {boat}). The improvement shown here is by Bill Gosper (August 1996). Dieter Leithner has since found (much larger) {oscillator}s of periods 44, 46 and 60 that can be used instead of the {Kok's galaxy}. For another periodic converter, see the glider-to-LWSS example in {queen bee shuttle pair}. However, many converters are {stable}. Examples of {elementary conduit} converters include {BFx59H}, {135-degree MWSS-to-G}, and {45-degree MWSS-to-G}. The earliest and simplest stable converters known are shown below. These are an HWSS-to-loaf, MWSS-to-beehive, and LWSS-to-blinker. These can serve as {memory cell}s, or as the first steps in constructing objects using {salvo}s.(        convoyA collection of {spaceship}s all moving in the same direction at the same speed. Convoys are usually not destroyed by the reactions that they cause. Compare {salvo}. For examples, see {reanimation}, {fly-by deletion} and {glider turner}. copperheadlThe following small c/10 {spaceship}, discovered by conwaylife.com forum user 'zdr' on 5 March 2016, using a simple depth-first search program. A {glider synthesis} was found on the same day. Later that same month Simon Ekstrom added a {sparky} {tagalong} for the copperhead to produce the {fireship}. This allowed for the construction of c/10 puffers and rakes.c/10 orthogonallyp10       Corder-KPrefix used for things involving {switch engine}s, after Charles Corderman. Corder engine= {switch engine} CordergunA {gun} firing {Cordership}s. The first was built by Jason Summers in July 1999, using a {glider synthesis} by Stephen Silver. CordershipAny {spaceship} based on {switch engine}s. These necessarily move at a speed of c/12 diagonally with a period of 96 or a multiple thereof. The first Cordership was constructed by Dean Hickerson in April 1991, using 13 switch engines. He soon reduced this to 10, and in August 1993 to 7. In July 1998 he reduced it to 6. In January 2004, Paul Tooke found the 3-engine {glide symmetric} Cordership shown below. At the end of 2017, Aidan F. Pierce discovered a clean {2-engine Cordership}. There is also an adjustable-length 4-engine Cordership found by Michael Simkin, made up of two identical or mirror-image 2-engine components. The leading pair of switch engines builds a block trail, which are then deleted by the trailing pair. Corderships generate {spark}s which can {perturb} other objects in many ways, especially gliders which can reach them from the side or from behind. Some perturbations reflect gliders back the way they came, and can be used for constructions such as the {caber tosser} and the {infinite glider hotel}. !# !#*,#%* ')- $'*+#%&*"$56"$56=>45=>'13456"&'()*01378!#+,14578!)+,234567"+,3#'()*()*$%#%"#!"$ !"#$#$    !! ! !!"" " " ""### ####$$$$%%%%&(())+,,,---- .....// / / / /////00 0000001 1 112 223 3 3 3 3 4 4 4 8 8 9 9?:cousins4This contains two copies of the {stillater} {rotor}.p3          coverJThe following {induction coil}. See {scrubber} for an example of its use. covered table= {cap}cow c p8 fuse !"%&)*-.1256   !"%&)*-.1256:;9;      !"#$%&'()*+,-./0123456789:   !"%&)*-.12569:   !"%&)*-.1256< CP pulsar = {pulsar}CP semi-cenarkA {colour-preserving} variant of Tanner Jacobi's century-based semi-Snark mechanism, the {semi-cenark}. See {CC semi-cenark} for the {colour-changing} version, or {semi-cenark} for repeat time details and an alternate initial catalyst.A                  CP semi-SnarkA period-multiplying {colour-preserving} {signal} {conduit} found by Tanner Jacobi in October 2017, producing one output {glider} for every two input gliders. It is made by replacing one of the eaters in a {Snark} with a {catalyst} found using {Bellman}. The catalyst causes the formation of a {tub} which requires a second glider to delete. However, this adds 5 ticks to the repeat time, so that it becomes 48. This is still 3 ticks faster than the {CC semi-Snark}.N             crab = {quarter}.craneThe following {spaceship} found by Nicolay Beluchenko in September 2005, a minor modification of a {tubeater} found earlier by Hartmut Holzwart. The wing is of the same form as in the {swan} and {Canada goose}.c/4 diagonallyp47                cross^Found by Robert Wainwright in October 1989. The members of this family are all {polyomino}es.p3crowd)Found by Dave Buckingham in January 1973.p3.                         crownThe p12 part of the following p12 {oscillator}, where it is {hassle}d by a {caterer}, a {jam} and a {HW emulator}. This oscillator was found by Noam Elkies in January 1995.I                                crucible = {cauldron}crystal^A regular growth that is sometimes formed when a stream of {glider}s, or other {spaceship}s, is fired into some junk. The most common example is initiated by the following collision of a glider with a {block}. With a glider stream of even {period} at least 82, this gives a crystal which forms a pair of {beehive}s for every 11 gliders which hit it. C-to-G= {century-to-glider converter}cuphookFound by Rich Schroeppel, October 1970. This is one of only three essentially different p3 {oscillator}s with only three cells in the {rotor}. The others are {1-2-3} and {stillater}. The above is the original form, but it can be made more compact:p3 curl= {loop}dartFound by David Bell, May 1992. A 25-glider recipe for the dart was found in December 2014 by Martin Grant and Chris Cain, making it the first glider-constructible c/3 spaceship.c/3 orthogonallyp3"            dead spark coilCompare {spark coil}.p1debris= {ash}.de Bruijn diagram= {de Bruijn graph}de Bruijn graphAs applied to Life, a de Bruijn graph is a graph showing which pieces can be linked to which other pieces to form a valid part of a Life pattern of a particular kind. For example, if we are interested in {still life}s, then we could consider 2x3 rectangular pieces and the de Bruijn graph would show which pairs of these can be overlapped to form 3x3 squares in which the centre cell remains unchanged in the next generation. David Eppstein's {search program} {gfind} is based on de Bruijn graphs. Deep CellDA pattern by Jared James Prince, based on David Bell's {unit Life cell}, in which each unit cell simulates two Life cells, in such a way that a Life universe filled with Deep Cells simulates two independent Life universes running in parallel. In fact, a Life universe filled with Deep Cells can simulate infinitely many Life universes, as follows. Let P_1, P_2, P_3, ... be a sequence of Life patterns. Set the Deep Cells to run a simulation of P_1 in parallel with a simulation of a universe filled with Deep Cells, with these simulated Deep Cells running a simulation of P_2 in parallel with another simulation of a universe filled with Deep Cells, with these doubly simulated Deep Cells simulating P_3 in parallel with yet another universe of Deep Cells, and so on. Deep Cell is available from {http://psychoticdeath.com/life.htm}.DemonoidThe first {self-constructing} diagonal spaceship. A 0{hd} Demonoid was completed by Chris Cain in December 2015, shortly after a much larger 10hd version was constructed the previous month in collaboration with Dave Greene. The 0hd spaceship fits in a bounding box about 55,000 cells square, and displaces itself by 65 cells diagonally every 438,852 generations. The first 0hd Demonoid was fired by a {gun}. No spaceship gun pattern had previously been completed before the first appearance of the actual spaceship. In June 2017 Dave Greene completed a much simpler {single-channel} Demonoid using a temporary {lossless elbow}, which displaces itself 79 cells diagonally every 1,183,842 ticks. This was an improvement in terms of design complexity, but not in terms of speed, population, or bounding box. However, all of these could be further optimized. A smaller Hashlife-friendly single-channel Demonoid design was completed in 2018. demultiplexerdA simple {Herschel} {circuit} consisting of three {eater1}s, found by Brice Due in August 2006. An input Herschel places a boat in a location accessible to an input glider. If the boat is present, a {one-time} {turner} reaction occurs and the glider is turned 90 degrees onto a new lane. If the Herschel and boat are removed from the above pattern, the glider passes cleanly through the circuit. It can be used as the "0" output of a one-bit {memory cell}, where the 90-degree output would be the "1" output. This was the method used to store presence or absence of neighbor {metacell}s in the {p1 megacell}.-              !demuxer= {demultiplexer}densitybThe density of a pattern is the limit of the proportion of live cells in a (2n+1)x(2n+1) square centred on a particular cell as n tends to infinity, when this limit exists. (Note that it does not make any difference what cell is chosen as the centre cell. Also note that if the pattern is finite then the density is zero.) There are other definitions of density, but this one will do here. In 1994 Noam Elkies proved that the maximum density of a stable pattern is 1/2, which had been the conjectured value. See the paper listed in the bibliography. Marcus Moore provided a simpler proof in 1995, and in fact proves that a {still life} with an m x n {bounding box} has at most (mn+m+n)/2 cells. But what is the maximum average density of an oscillating pattern? The answer is conjectured to be 1/2 again, but this remains unproved. The best upper bound so far obtained is 8/13 (Hartmut Holzwart, September 1992). The maximum possible density for a {phase} of an oscillating pattern is also unknown. An example with a density of 3/4 is known (see {agar}), but densities arbitrarily close to 1 may perhaps be possible.dependent conduitA {Herschel conduit} in which the input {Herschel} interacts with catalysts in the first few ticks. The standard interaction actually starts at T=-3, before the Herschel is completely formed. Compare {independent conduit}. The Herschel is prevented from emitting its {first natural glider}. This is useful in cases where the previous conduit cannot survive a first natural glider emitted from its output Herschel. This term is somewhat confusing, since it is actually the previous conduit that depends on the dependent conduit to suppress the problematic glider. Dependent conduits such as the {F166} and {Lx200} do not actually depend on anything. They can be freely connected to any other conduits that fit, as long as the output Herschel evolves from its standard great-grandparent. As of this writing, the {Fx158} is the only known case where a conduit's output Herschel has an alternate great-grandparent, which is incompatible with dependent conduits' initial transparent block.destructive read:The most common type of test reaction in {memory cell} circuitry. Information is stored in a memory cell by placing objects in known positions, or by changing the state of a stable or periodic {toggle circuit}. A destructive-read test consists of sending one or more {signal}s to the memory cell. A distinct output signal is produced for each possible state of the memory cell, which is reset to a known "zero" or "rest" state. See for example {boat-bit}, {keeper}, and {demultiplexer}. To permanently store information in a destructive-read memory cell, the output signal(s) must be used, in part, to send appropriate signals back to the memory cell to restore its state to its previous value. With output looped back to input, this larger composite circuit then effectively becomes a {non-destructive read} memory cell.destructor armA dedicated {construction arm} in the {Gemini} spaceship, used only for removing previously active {circuit}ry once it is no longer needed. More generally, any circuitry in a self-constructing pattern dedicated exclusively to cleanup. D-heptomino = {Herschel}diamond= {tub} diamond ring!Found by Dave Buckingham in 1972.p3(                diehard<Any pattern that vanishes, but only after a long time. The following example vanishes in 130 generations, which is probably the limit for patterns of 7 or fewer cells. Note that there is no limit for higher numbers of cells. E.g., for 8 cells we could have a glider heading towards an arbitrarily distant blinker. dinner table#Found by Robert Wainwright in 1972.p12"             dirtyOpposite of {clean}. A reaction which produces a large amount of complicated junk which is difficult to control or use is said to be dirty. Many basic {puffer engine}s are dirty and need to be {tame}d by accompanying {spaceship}s in order to produce clean output. Similarly, a dirty {conduit} is one that does not recover perfectly after the passage of a {signal}; one or more extra {ash} objects are left behind (or more rarely a {catalyst} is damaged) and additional signals must be used to clean up the circuit before it can be re-used.diuresisFound by David Eppstein in October 1998. His original stabilization used {pentadecathlon}s. The stabilization with complicated {still life}s shown here (in two slightly different forms) was found by Dean Hickerson the following day. The name is due to Bill Gosper (see {kidney}).p90y                       dockThe following {induction coil}. dominooThe 2-cell {polyomino}. A number of objects, such as the {HWSS} and {pentadecathlon}, produce domino {spark}s.dormantAn object that is either stable or oscillates without producing any output, until it is {trigger}ed by an appropriate signal, which then produces some desired action. For example, {freeze-dried} objects are dormant until the arrival of a particular glider. do-see-doThe following reaction, found by David Bell in 1996, in which two {glider}s appear to circle around each other as they are reflected 90 degrees by a {twin bees shuttle}. Four copies of the reaction can be used to create a p92 glider loop which repeats the do-see-do reaction forever.B57566010.0./        !! ""## ####$$ $ $ $$$8%double-barrelledZOf a {gun}, emitting two streams of {spaceship}s (or {rake}s) every period. For examples, see {B-52 bomber}, {Simkin glider gun}, and {p246 gun}. In most cases, the two streams are alternately emitted 1/2 period apart. It is also possible for the two streams to be emitted simultaneously, as in this double-barrelled glider gun by Bill Gosper:$  0101          2double block reactionA certain reaction that can be used to stabilize the {twin bees shuttle} (qv). This was discovered by David Bell in October 1996. The same reaction sometimes works in other situations, as shown in the following diagram where a pair of blocks eats an {R-pentomino} and a {LWSS}. (The LWSS version was known at least as early 1994, when Paul Callahan saw it form spontaneously as a result of firing an LWSS stream at some random junk.)      double catererOFound by Dean Hickerson, October 1989. Compare {caterer} and {triple caterer}.p3A                               double ewe1Found by Robert Wainwright before September 1971.p36                                double wing2= {moose antlers}. This term is no longer in use.dovexThe following {induction coil}, found in 2015 to be a possible active reaction for the input or output of a {converter}. down boat with tail= {cis-boat with tail}drShort identifier for Dean Hickerson's 'drifter' search program, used at various times to find {wire}s, {eater}s, higher-period {billiard table configuration}s, and related {signal}-carrying and signal-processing mechanisms. See also {drifter}.dragonThis {spaceship}, discovered by Paul Tooke in April 2000, was the first known {c/6 spaceship}. With 102 cells, it was the smallest known orthogonal c/6 spaceship until Hartmut Holzwart discovered {56P6H1V0} in April 2009.c/6 orthogonallyp6                                                               drain trap.= {paperclip}. This term is no longer in use.D read= {destructive read}dried= {freeze-dried}.drifterA perturbation moving within a stable pattern. Dean Hickerson has written a {search program} to search for drifters, with the hope of finding one which could be moved around a track. Because drifters can be very small, they could be packed more tightly than {Herschel}s, and so allow the creation of {oscillator}s of periods not yet attained, and possibly prove that Life is {omniperiodic}. Hickerson has found a number of components towards this end, but it has proved difficult to change the direction of movement of a drifter, and so far no complete track has been found. However, Hickerson has had success using the same program to find {eater}s with novel properties, such as {sparking eater}s and the ones shown in {diuresis}. dual 1-2-3-4= {Achim's p4}duopletA diagonal two-bit spark produced by many oscillators and eater reactions. Among other uses, it can reflect gliders 90 degrees. The following pattern shows an {eater5} eating gliders and producing duoplets which are then used to reflect a separate glider stream. If only one glider is present, the eater5 successfully absorbs it, so this mechanism may be considered to be a simple AND gate.        dying sparkSSee {spark}. A spark by definition dies out completely after some number of ticks.early universe3Conway's somewhat confusing term for {sparse Life}.eaterAny {still life} that has the ability to interact with certain patterns without suffering any permanent damage. (If it doesn't suffer even temporary damage then it may be referred to as a {rock}.) The {eater1} is a very common eater, and the term "eater" is often used specifically for this object. Other eaters include {eater2}, {eater3}, {eater4}, and {eater5}, and many hundreds of others are known. Below is a complex eater found by Dean Hickerson in 1998 using his {dr} {search program}. It takes 25 {tick}s to recover after feasting on a glider: Some common {still life}s can act as eaters in some situations, such as the {block}, {ship}, and {tub}. In fact the block was the first known eater, being found capable of eating beehives from a {queen bee}.:                            eater1Usually simply called an {eater}, and also called a fishhook. This eater can be constructed using a simple two-glider collision, as shown in {stamp collection}. It is often modified in various ways, or {weld}ed to other objects, to allow tighter packing of {circuit}s or to allow a {signal} {stream} to pass close by. See {clearance} for an eater1 variant that is 1{hd} shorter to the southeast than the standard fishhook form. An eater1 can also be used as a 90-degree {one-time} {turner}. Its ability to eat various objects was discovered by Bill Gosper in 1971. The fishhook eater can consume a glider, a {LWSS}, and a {MWSS} as shown below. It is not able to consume an {HWSS}, however. See {honey bit} or {killer toads} for that.p1eater2 This {eater} was found by Dave Buckingham in the 1970s. Mostly it works like the ordinary {eater1} but with two slight differences that make it useful despite its size: it takes longer to recover from each bite, and it can eat objects appearing at two different positions. The first property means that, among other things, it can eat a {glider} in a position that would destroy an {eater1}. This novel glider-eating action is occasionally of use in itself, and combined with the symmetry means that an eater2 can eat gliders travelling along four adjacent glider {lane}s, as shown below. The following eater2 variant (Stephen Silver, May 1998) can be useful for obtaining smaller {bounding box}es. A more compact variant with the same purpose can be seen under {gliderless}.p1eater3This large symmetric {eater}, found by Dave Buckingham, has a very different eating action from the {eater1} and {eater2}. The {loaf} can take bites out things, being flipped over in the process. The rest of the object merely flips it back again.p1           eater4Another {eater} by Dave Buckingham, which he found in 1971, but did not recognize as an eater until 1975 or 1976. It can't eat {glider}s, but it can be used for various other purposes. The four NE-most centre cells regrow in a few generations after being destroyed by taking a bite out of something, such as suppressing half of a developing {traffic light} as it does in the {p29 pentadecathlon hassler}.p1(     eater5A compound {eater} that can eat {glider}s coming from two different directions. Also called the tub-with-tail eater (TWIT), it is often placed along the edges of glider {lane}s to suppress unwanted gliders in {conduit}s. Below is the standard form, a compact form with a {long hook}, and an often-useful conjoined form found with {Bellman}. The {sidesnagger} is a Spartan constellation that has a similar glider-absorbing function, using a {loaf}. See also {7x9 eater}. With gliders from either direction, the eater5's eating reaction creates a {spark} that can be used to reflect other gliders. See the example pattern in {duoplet}, or advance any of the topmost three gliders in the above pattern by two {tick}s.p1T                                                !eater/block frob,Found by Dave Buckingham in 1976 or earlier.p4   eater-bound pond&= {biting off more than they can chew}eater-bound Z-hexomino = {pentoad}eater eating eater= {two eaters} eater plug*Found by Robert Wainwright, February 1973.p2 eaters plus= {French kiss} ecologistoThis consists of the classic {puffer train} with a {LWSS} added to suppress the debris. See also {space rake}.c/2 orthogonallyp20G                         edge-repair spaceshipA {spaceship} which has an edge that possesses no {spark} and yet is able to {perturb} things because of its ability to repair certain types of damage to itself. The most useful examples are the following two small p3 {c/3 spaceship}s: These were found by David Bell in 1992, but the usefulness of the edge-repair property wasn't recognised until July 1997. The following diagram (showing an edge-repair spaceship deleting a {Herschel}) demonstrates the self-repairing action. In October 2000, David Bell found that a {T-tetromino} component of a {c/4 spaceship} can also be self-repairing. Stephen Silver noticed that it could be used to delete beehives and, in November 2000, found the smallest known c/4 spaceship with this edge-repair component - in fact, two copies of the component:3" !"$%&   '   !%&   ( edge shooterA {gun} or {signal} {circuit} that fires its gliders (or whatever) right at the edge of the pattern, so that it can be used to fire them closely parallel to others. This is useful for constructing complex guns. Compare {glider pusher}, which can in fact be used for making edge shooters. The following diagram shows a p46 edge shooter found by Paul Callahan in June 1994. Stable edge shooters became possible with the development of {Herschel circuit}ry. For example, {NW31}, {BNE14T30}, {RNE-19T84}, and the high-{clearance} {Fx119 inserter} are often used in {shotgun}s for complex salvos. Composite edge-shooter circuits with arbitrarily high clearance can be constructed.P !%&'"$(!"$%) &')' &' &'* edge sparkgA {spark} at the side of a {spaceship} that can be used to {perturb} things as the spaceship passes by. edge sparker6A {spaceship} that produces one or more {edge spark}s.edgyIn {slow salvo} terminology, an edgy glider construction recipe is one that places its final product at or very near the edge of its {construction envelope}. Similarly, an edgy {factory} will place its output object in an accessible location near the edge of its {reaction envelope}.egg.= {non-spark}. This term is no longer in use. E-heptomino2Name given by Conway to the following {heptomino}.elbowrDepending on context, this term may refer to a {signal elbow} or a {construction elbow}. See also {elbow ladder}. elbow ladderScot Ellison's name for the type of pattern he created in which one or more {glider}s shuttle back and forth (using the {kickback reaction}) deleting the output gliders from a pair of {slide gun}s.elbow operationtA recipe, usually a {salvo} of {glider}s travelling on one or more {construction lane}s, that collides with an {elbow} {constellation} and performs one of the standard transformations on it: {push}, {pull}, or {fire} for simple construction arms, along with possible construct, duplicate-elbow, or delete-elbow ops for more complicated systems. See {construction elbow}.electric fence:A stabilization of {ants}. Dean Hickerson, February 1993.p5  $%  %),39:  %'(),-.249 &*+/14;    '(,/13467:;  "#()+,/1468   !%&'-./02346:;   !%&')*-249<         " # * 7 ; <       * 3 4 6       ' ( * ,   ( + , & ( &'= elementaryNot reducible to a combination of smaller parts. Elementary {spaceship}s in particular are usually those found by search programs, and they can't be subdivided into smaller spaceships, tagalongs, and supporting reactions, as contrasted with engineered {macro-spaceship}s.elementary conduitA {conduit} with no recognizable active signal stage besides its input and output. An early example still very commonly used is Buckingham's {BFx59H}, which transforms a {B-heptomino} into an inverted {Herschel} in 59 ticks. The BFx59H elementary conduit is a component in many of the original {universal} {toolkit} of Herschel conduits. An extension of the same naming convention is used for elementary conduits, with the first and last letters of the name specifying the input and output {signal} objects. As with Herschels, an arbitrary orientation and center point is chosen for each object. "Fx" means the signal moves forward and produces a mirror-image output. See {Herschel conduit} for further details. Theoretically an elementary conduit may become a composite conduit, if another conduit can be found that shares the beginning or end of the conduit in question. In practice this happens only rarely, because many of the most likely branch points have already been identified: {glider} (G), {LWSS} (L) or {MWSS} (M), {Herschel} (H), {B-heptomino} (B), {R-pentomino} (R), {pi-heptomino} (P), {queen bee shuttle} (Q), {century} or {bookend} (C), {dove} (D), and {wing} (W). A {Herschel descendant} might qualify, due to the elementary conduit that can be seen in the {p184 gun}. However, there are very few simple conduits that produce Herschel descendants without Herschels, so in practice this is not a useful branch point.elevenerp1  Elkies' p5Found by Noam Elkies in 1997.p5 emuDave Buckingham's term for a {Herschel loop} that does not emit {glider}s (and so is "flightless"). All known Herschel loops of periods 52, 57, 58, 59 and 61 are emus. See also {Quetzal}.emulatorgAny one of three p4 oscillators that produce {spark}s similar to those produced by {LWSS}, {MWSS} and {HWSS}. See {LW emulator}, {MW emulator} and {HW emulator}. Larger emulators are also possible, but they require stabilizing objects to suppress their {non-spark}s and so are of little use. The emulators were discovered by Robert Wainwright in June 1980.engine[The active portion of an object (usually a {puffer} or {gun}) which is considered to actually produce its output, and which generally permits no variation in how it works. The other parts of the object are just there to support the engine. For examples, see {puffer train}, {Schick engine}, {blinker puffer}, {frothing puffer} and {line puffer}. enginelessA {rake} or {puffer} which does not contain a specific {engine} for its operation. Instead it depends on perturbations of gliders or other objects by passing spaceships. The period of such objects is often adjustable, and in some cases the speed as well. An early example was the creation of c/5 rakes in September 1997, using gliders circulating among a convoy of c/5 spaceships. More recently, the passing spaceships themselves are also constructed, as in the {Caterloopillar}. en retard&Found by Dave Buckingham, August 1972.p3(             Enterprise$Found by Dean Hickerson, March 1993.c/4 diagonallyp4M                                  envelope1See {construction envelope}, {reaction envelope}.EurekaA {pre-pulsar} {shuttle} found by Dave Buckingham in August 1980. A variant is obtained by shifting the top half two spaces to either side.p30          evolutionThe process or result of running one or more generations of an object. For example, a row of 10 cells evolves into a {pentadecathlon}.evolutionary factorFor an unstable pattern, the time to stabilization divided by the initial {population}. For example, the {R-pentomino} has an evolutionary factor of 220.6, while {bunnies} has an evolutionary factor of 1925.777... The term is no longer in use.exhaustThe debris or {smoke} left behind by a {puffer}, especially if the debris is {dirty} and takes many {generation}s to settle. The term is not usually used for the objects created by {clean} puffers.exponential filterA {toolkit} developed by Gabriel Nivasch in 2006, enabling the construction of patterns with asymptotic population growth matching O((log log ... log(t))) for any number of nested log operations. See also {quadratic filter}, {recursive filter}.exposure= {underpopulation} extensible#A pattern is said to be extensible if arbitrarily large patterns of the same type can be made by repeating parts of the original pattern in a regular way. For examples, see {p6 shuttle}, {pentoad}, {pufferfish spaceship}, {snacker}, {wavestretcher}, {wicktrailer} and {branching spaceship}.extra extra long = {long^4} extra long = {long^3}extremely impressive&Found by Dave Buckingham, August 1976.p6      extruderSee {traffic lights extruder}. A {single-channel} constructor arm has also been programmed to extrude a growing {wick} consisting of a chain of {Snark}s, again working from the stationary {fencepost} end of the wick with no need for a {wickstretcher} component.F116An {elementary conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in February 1997. After 116 ticks, it produces a {Herschel} at (32, 1) relative to the input. Its {recovery time} is 138 ticks; this can be reduced to 120 ticks by adding extra mechanisms to suppress the internal glider. It is {Spartan} only if the following conduit is a {dependent conduit}, so that the {weld}ed {FNG} eater can be removed. A {ghost Herschel} in the pattern below marks the output location:&        !""    #F117A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in July 1996. It is made up of two {elementary conduit}s, {HFx58B} + {BFx59H}. After 117 ticks, it produces a {Herschel} at (40, -6) relative to the input. Its {recovery time} is 63 ticks. It can be made {Spartan} by replacing the {snake} with an {eater1} in one of two orientations. A {ghost Herschel} in the pattern below marks the output location:,         *   * * + , , -F166A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in May 1997. It is composed of two {elementary conduit}s, HFx107B + {BFx59H}. The F166 and {Lx200} conduits are the two original {dependent conduit}s (several more have since been discovered). After 166 ticks, it produces a {Herschel} at (49, 3) relative to the input. Its {recovery time} is 116 ticks. A {ghost Herschel} in the pattern below marks the output location: The F166 can be made {Spartan} by replacing the {snake} with an {eater1} in one of two orientations. The input shown here is a {Herschel great-grandparent}, since the input reaction is catalysed by the {transparent} block before the Herschel's standard form can appear.G!""!!"       $ % 5  $ % 5 5 6 7 7 .// ,-. ,8F171VAn {elementary conduit}, the seventeenth {Herschel conduit}, discovered by Brice Due in August 2006 in a search using only {eater}s as {catalyst}s. This was the first new Herschel conduit discovery since 1998. After 171 ticks, it produces a {Herschel} at (29, -17) relative to the input. A {ghost Herschel} in the pattern below marks the output location: The conduit's {recovery time} is 227 ticks, slower than many of the original sixteen conduits because of the delayed destruction of a temporary blinker, though the circuit itself is clearly {Spartan}. The recovery time can be improved to 120 ticks by adding {sparker}s of various periods to suppress the blinker. See {clock} for a period-2 example. The central eater in the group of three to the northwest can be removed to release an additional {glider} output signal on a {transparent} {lane}.0                    ! ! !"!#factoryAnother word for {gun}, but not used in the case of glider guns. The term is also used for a pattern that repeatedly manufactures objects other than {spaceship}s or {rake}s. In this case the new objects do not move out of the way, and therefore must be used up in some way before the next one is made. The following shows an example of a p144 gun which consists of a p144 block factory whose output is converted into gliders by a p72 oscillator. This gun is David Bell's improvement of the one Bill Gosper found in July 1994. The p72 oscillator is by Robert Wainwright in 1990, and the block factory is {Achim's p144} minus one of its stabilizing blocks. For a block factory using stable components and triggered by an input {Herschel}, see also {keeper}._1212)*(+)*$%&$&  $%& $ %  # $ %   # %   # $ %   ! 1212  3familiar fours(Common patterns of four identical objects. The five commonest are {traffic light} (4 blinkers), {honey farm} (4 beehives), {blockade} (4 blocks), {fleet} (4 ships, although really 2 ship-ties) and {bakery} (4 loaves, although really 2 bi-loaves). Also sometimes included is {four skewed blocks}.fanoutA mechanism that emits two or more objects of some type for each one that it receives. Typically the objects are {glider}s or {Herschel}s; {glider duplicator}s are a special case.Fast Forward Force FieldThe following reaction found by Dieter Leithner in May 1994. In the absence of the incoming LWSS the gliders would simply annihilate one another, but as shown they allow the LWSS to advance 11 spaces in the course of the next 6 generations. The illusion of super-light-speed travel is caused by an LWSS that is always created, but is then destroyed in some cases, by a signal catching up to it from behind that necessarily never travels faster than the {speed of light}. It is not possible to make any use of the apparent super-light-speed signal. The front end of an output LWSS can't be distinguished from the alternative dying {spark} output until several more ticks have passed. Not surprisingly, this extra time is enough to drop the average speed of information transmission safely below c. Leithner named the Fast Forward Force Field in honour of his favourite science fiction writer, the physicist Robert L. Forward. See also {star gate} and {speed booster}.    fate0The result of evolving a pattern until its final behaviour is known. This answers such questions such as whether or not the pattern remains finite, what its growth rate is, what {period} the final state may settle into, and what its final {census} is. All small Life objects seem to eventually settle down into a mix of oscillators, simple spaceships, and occasionally small puffers. See {methuselah}, {soup}, {ash}. Most sufficiently large random patterns are expected to grow forever due to the production of {switch engine}s at their boundary. Engineered Life objects - and therefore also sufficiently large and unlikely random patterns - can have more interesting behaviour, such as {breeder}s, {sawtooth}s, and prime calculators. Some objects have even been constructed or designed having an {unknown fate}.father = {parent}fd"Abbreviation for {full diagonal}s.featherweight spaceship = {glider} fencepost0Any pattern that stabilizes one end of a {wick}.Fermat prime calculatorA pattern constructed by Jason Summers in January 2000 that exhibits {infinite growth} if and only if there are no Fermat primes greater than 65537. The question of whether or not it really does exhibit infinite growth is therefore equivalent to a well-known and long-standing unsolved mathematical problem. It will, however, still be growing at generation 10^2585827975. The pattern is based on Dean Hickerson's {primer} and {caber tosser} patterns and a p8 {beehive} {puffer} by Hartmut Holzwart. F-heptomino2Name given by Conway to the following {heptomino}.figure-83A {domino} {sparker} found by Simon Norton in 1970.p8filterAny {oscillator} used to delete some but not all of the {spaceship}s in a stream. An example is the {blocker}, which can be positioned so as to delete every other {glider} in a stream of period 8n+4, and can also do the same for {LWSS} streams. Other examples are the {MW emulator} and {T-nosed p4} (either of which can be used to delete every other LWSS in a stream of period 4n+2), the {fountain} (which does the same for {MWSS} streams) and a number of others, such as the p6 {pipsquirter}, the {pentadecathlon} and the p72 oscillator shown under {factory}. Another example, a p4 oscillator deleting every other HWSS in a stream of period 4n+2, is shown below. (The p4 oscillator here was found, with a slightly larger {stator}, by Dean Hickerson in November 1994.)                                                         filter streamA {stream} of {spaceship}s in which there are periodic gaps in the stream. This can thin out another crossing stream by deleting the {spaceship}s in the second stream except where the gaps occur. The filter stream is not affected by the deletions so that the same stream can thin out multiple other streams. The {Caterpillar} uses filter streams of {MWSS}s in which there is a gap every 6 spaceships. Here is part of a filter stream that thins a glider stream by 2/3:; ! !'(& ' ( ./-./,:*.8</=*/8=+,-./9:;<=>finger A protruding cell in an {oscillator} or {dying spark}, with the ability to modify a nearby active reaction. Like a {thumb}, a finger cell appears at the edge of a reaction envelope and is the only live cell in its row or column. The finger spark remains alive for two ticks before dying, whereas a thumb cell dies after one tick. Because the key cell is kept alive for an extra tick, an alternate technical term is "held (orthogonal) bit spark". A "held diagonal bit spark" is not possible in B3/S23 for obvious reasons.fireAn encoded signal used in combination with {push} and {pull} {elbow operation}s in a simple {construction arm}. When a FIRE signal is sent, the construction-arm elbow produces an output glider, usually at 90 degrees from the construction arm. This terminology is generally used when there is only a single recipe for such a glider output, or only one recipe for each glider colour (e.g., FIRE WHITE, FIRE BLACK).fireshipA variant of the {copperhead} with a trailing component that emits several large {spark}s, discovered by Simon Ekstrom on 20 March 2016. The interaction between the copperhead and the additional component is minimal enough that the extension technically fits the definition of a {tagalong}. However, the extension slightly modifies two of the {phase}s of the spaceship, starting two ticks after the phase shown below, so it's also valid to classify the fireship as a distinct spaceship.c/10 orthogonallyp106           fire-spitting,Found by Nicolay Beluchenko, September 2003.p3   first natural gliderThe glider produced at T=21 during the {evolution} of a {Herschel}. This is the most common signal output from a {Herschel conduit}.fishA generic term for {LWSS}, {MWSS} and {HWSS}, or, more generally, for any {spaceship}. In recent years {*WSS} is much more commonly used to refer to the small orthogonal c/2 spaceships.fishhook = {eater1}fleet&A common formation of two {ship-tie}s.p1    flip-flopAny p2 {oscillator}. However, the term is also used in two more specific (and non-equivalent) senses: (a) any p2 oscillator whose two {phase}s are mirror images of one another, and (b) any p2 oscillator in which all {rotor} cells die from {underpopulation}. In the latter sense it contrasts with {on-off}. The term has also been used even more specifically for the 12-cell flip-flop shown under {phoenix}. flip-flops5Another name for the flip-flop shown under {phoenix}.flipperWAny {oscillator} or {spaceship} that forms its mirror image halfway through its period.flotillaA {spaceship} composed of a number of smaller interacting spaceships. Often one or more of these is not a true spaceship and could not survive without the support of the others. The following example shows an {OWSS} escorted by two {HWSS}.9                     fly~A certain c/3 {tagalong} found by David Bell, April 1992. Shown here attached to the back of a small spaceship (also by Bell). !                                                             ! "fly-by deletion2A reaction performed by a passing {convoy} of {spaceship}s which deletes a common stationary object without harming the convoy. Fly-by deletion is often used in the construction of {puffer}s and {spaceship}s to clean up unwanted debris. For c/2 convoys this is not usually difficult since the {LWSS}, {MWSS}, and {HWSS} {spaceship}s have such useful {spark}s. However, some objects are more difficult to delete. For example, deleting a {tub} appears to require an unusual p4 spaceship. The deletion of a {pond} appears to require a convoy which is 89 cells in width containing a very unusual p4 spaceship which has 273 cells. There are small objects which have no known fly-by deletion reactions. However, as in the case of {reanimation}, hitting them with the output of {rake}s is an effective brute force method.B                              !flying machine= {Schick engine}FNG= {first natural glider}. fore and back<Compare {snake pit}. Found by Achim Flammenkamp, July 1994.p2forward glidervA {glider} which moves at least partly in the same direction as the {puffer}(s) or {spaceship}(s) under consideration.fountainkFound by Dean Hickerson in November 1994, and named by Bill Gosper. See also {filter} and {superfountain}.p4?                              four skewed blocksThe following {constellation}, sometimes considered to be one of the {familiar fours}. This is most commonly created by a symmetric {2-glider collision}:p1      fourteenerp1foxTThis is the smallest asymmetric p2 oscillator. Found by Dave Buckingham, July 1977.p2  freeze-driedZA term used for a {glider constructible} {seed} that can activated in some way to produce a complex object. For example, a "freeze-dried salvo" is a constellation of constructible objects which, when {trigger}ed by a single glider, produces a unidirectional glider {salvo}, and nothing else. Freeze-dried salvos can be useful in {slow salvo} constructions, especially when an active circuit has to destroy or reconstruct itself in a limited amount of time. Gradual modification by a {construction arm} may be too slow, or the circuit doing the construction may itself be the object that must be modified. The concept may be applied to other types of objects. For example, one possible way to build a gun for a {waterbear} would be to program a construction arm to build a freeze-dried waterbear seed, and then trigger it when the construction is complete. French kissFound by Robert Wainwright, July 1971. For many years this was one of the best-known small oscillators with no known {glider synthesis}. In October 2013 Martin Grant completed a 23-glider construction.p3   frog II'Found by Dave Buckingham, October 1972.p3-              frothing pufferOA frothing puffer (or a frothing spaceship) is a {puffer} (or {spaceship}) whose back end appears to be unstable and breaking apart, but which nonetheless survives. The {exhaust} festers and clings to the back of the puffer/spaceship before breaking off. The first known frothing puffers were c/2, and most were found by slightly modifying the back ends of p2 spaceships. A number of these have periods which are not a multiple of 4 (as with some {line puffer}s). Paul Tooke has also found c/3 frothing puffers. The following p78 c/2 frothing puffer was found by Paul Tooke in April 2001.                                              !frothing spaceshipSee {frothing puffer}.frozen= {freeze-dried}. full diagonalDiagonal distance measurement, abbreviated "fd", often appropriate when a {construction arm} {elbow} or similar diagonally-adjustable mechanism is present.fumarolepFound by Dean Hickerson in September 1989. In terms of its 7x8 bounding box this is the smallest p5 oscillator.p5fuseA {wick} {burn}ing at one end. For examples, see {baker}, {beacon maker}, {blinker ship}, {boat maker}, {cow}, {harvester}, {lightspeed wire}, {pi ship}, {reverse fuse}, {superstring} and {washerwoman}. Useful fuses are usually {clean}, but see also {reburnable fuse}. A fuse can {burn} arbitrarily slowly, as demonstrated by the example {Blockic} fuse below. A {signal}, alternating between {glider} and {MWSS} form, travels up and down between two rows of blocks in a series of {one-time} {turner} reactions. The spacing shown here causes the fuse to burn 24 cells to the right every 240 generations, for a speed of c/10. Moving the bottom half further from the top half by any even number of cells will slow down the burning even further. !"  !"&'56&'1256+,12+,   $ % * +   $ % * + 01670167 78  %&78 %&)*23    ) * 2 3 ##-#.#$$-$.$9%Fx119An {elementary conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in September 1996. After 119 ticks, it produces an inverted {Herschel} at (20, 14) relative to the input. Its recovery time is 231 ticks; this can be reduced somewhat by suppressing the output Herschel's glider, or by adding extra {catalyst}s to make the reaction settle more quickly. A {ghost Herschel} in the pattern below marks the output location:         Fx119 inserterA {Herschel-to-glider} {converter} and {edge shooter} based on an {Fx119} Herschel conduit: This edge shooter has an unusually high 27{hd} clearance, one of the highest known for a single small component. The only known higher-clearance edge shooters are injectors making use of multiple interacting spaceships. This makes the Fx119 inserter ideal for the construction of wide {convoy}s whose total width can fit within its clearance distance. The component creates a large cloud of {smoke} behind its emitted glider which lasts for over 90 generations. In spite of this, many tightly packed convoys can be made by injecting later gliders behind others in the convoy, helped along by the insertion reaction which is able to catch up to the existing gliders. The Fx119 inserter can place a glider on the same lane as a passing glider and as close as 15 ticks behind, which is only one step away from the minimum possible following distance./                      Fx153A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in February 1997. It is made up of two {elementary conduit}s, HF94B + {BFx59H}. After 153 ticks, it produces an inverted {Herschel} at (48, -4) relative to the input. Its {recovery time} is 69 ticks. It can be made {Spartan} by replacing the {snake} with an {eater1} in one of two orientations. A {ghost Herschel} in the pattern below marks the output location:742 3 4 ! " 2  ! " 2             5Fx158An {elementary conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in July 1996. After 158 ticks, it produces an inverted {Herschel} at (27, -5) relative to the input. Its {recovery time} is 176 ticks. It is the only known small conduit that does not produce its output Herschel via the usual {Herschel great-grandparent}, so it cannot be followed by a {dependent conduit}. A {ghost Herschel} in the pattern below marks the output location:I                     Fx176A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in October 1997. It is made up of three {elementary conduit}s, HF95P + PF35W + WFx46H. After 176 ticks, it produces an inverted {Herschel} at (45, 0) relative to the input. The {recovery time} of the standard form shown here is 92 ticks, but see the {PF35W} entry for a variant discovered in November 2017 that lowers the repeat time to 73 ticks. A {ghost Herschel} in the pattern below marks the output location.W         )***,+-,0101$%1$%/01//     !!""""## #!#$ $!$%%2&Fx77An {elementary conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in August 1996. After 77 ticks, it produces an inverted {Herschel} at (25, -8) relative to the input. Its {recovery time} is 61 ticks; this can be reduced slightly by suppressing the output Herschel's glider, as in the {L112} case. A {pipsquirter} can replace the blinker-suppressing eater to produce an extra glider output. It is one of the simplest known {Spartan} conduits, and one of the few {elementary conduit}s in the original set of sixteen. In January 2016, Tanner Jacobi discovered a {Spartan} method of extracting an extra glider output (top variant below). A {ghost Herschel} marks the output location for each variant.C            &'''()))))*****+,011222399::;<<= G4 receiverNAn alternate {Herschel receiver} discovered by Sergei Petrov on 28 December 2011, using his previous {glider to 2 blocks} {converter}. In the pattern below the {Herschel} output is marked by a {ghost Herschel}. A {glider} also escapes to the northwest. For an explanation of the "G4" describing the {tandem glider} input, see {Gn}.E " !!&  $ % &   #  # $ &'7  &'7  7899  !"":Gabriel's p138DThe following {oscillator} found by Gabriel Nivasch in October 2002.p138,                   galaxy= {Kok's galaxy} Game of Life= {Life}Game of Life NewsA blog reporting on new Life discoveries, started by Heinrich Koenig in December 2004, currently found at {http://pentadecathlon.com/lifenews/}.Garden of EdenA configuration of ON and OFF cells that can only occur in generation 0. (This term was first used in connection with cellular automata by John W. Tukey, many years before Life.) It was known from the start that there are Gardens of Eden in Life, because of a theorem by Edward Moore that guarantees their existence in a wide class of cellular automata. Explicit examples have since been constructed, the first by Roger Banks, et al. at MIT in 1971. This example was 9 x 33. In 1974 J. Hardouin-Duparc et al. at the University of Bordeaux 1 produced a 6 x 122 example. The following shows a 12 x 12 example found by Nicolay Beluchenko in February 2006, based on a 13 x 12 one found by Achim Flammenkamp in June 2004. Below is a 10x10 Garden of Eden found by Marijn Heule, Christiaan Hartman, Kees Kwekkeboom, and Alain Noels in 2013 using SAT-solver techniques. An exhaustive search of 90-degree rotationally symmetric 10x10 patterns was possible because the symmetry reduces the number of unknown cells by a factor of four. Steven Eker has since found several asymmetrical Gardens of Eden that are slightly smaller than this in terms of bounding box area. Patterns have also been found that have only Garden of Eden {parent}s. For related results see {grandparent}.P                           Geminikc/33699586 obliquely, p33699586) The first {self-constructing} spaceship, and also the first {oblique} spaceship. It was made public by Andrew Wade on 18 May 2010. It was the thirteenth explicitly constructed spaceship velocity in Life, and made possible an infinite family of related velocities. The Gemini spaceship derives its name from the Latin "gemini", meaning twins, describing its two identical halves, each of which contains three Chapman-Greene {construction arm}s. A tape of gliders continually relays between the two halves, instructing each to delete its parent and construct a daughter configuration. (5120,1024 Gemini pufferSee {Pianola breeder}.GeminoidA type of self-constructing circuitry that borrows key ideas from Andrew Wade's {Gemini} spaceship, but with several simplifications. The main feature common to the Gemini spaceship is the construction recipe encoding method. Information is stored directly, and much more efficiently, in the timings of moving gliders, rather than in a static tape with 1s and 0s encoded by the presence of small stationary objects. Unlike the original Gemini, Geminoids have {ambidextrous} construction arms, initially using glider pairs on two lanes separated by 9{hd}, 10hd, or 0hd. The design was the basis for the {linear propagator} and the {Demonoid}s. A more recent development is a Geminoid toolkit using a {single-channel} construction arm, which allows for the possibility of multiple elbows with no loss of efficiency, or the construction of temporary lossless elbows. Compare {slow elbow}. Other new developments that could be considered part of the extended "Geminoid" toolkit include {freeze-dried} construction salvos and seeds, used when objects must be built within a short time window, and self-destruct circuits, which are used as an alternative to a {destructor arm} to clean up temporary objects in a similarly short window. generationDThe fundamental unit of time. The starting pattern is generation 0.germ)Found by Dave Buckingham, September 1972.p3    gfind.A program by David Eppstein which uses {de Bruijn graph}s to search for new {spaceship}s. It was with gfind that Eppstein found the {weekender}, and Paul Tooke later used it to find the {dragon}. It is available at {http://www.ics.uci.edu/~eppstein/ca/gfind.c} (C source code only). Compare {lifesrc}.ghost Herschel?A dying {spark} made by removing one cell from the {Herschel} heptomino. This particular spark has the advantage that, when placed in a conduit to mark the location of an input or output Herschel, it disappears cleanly without damaging adjacent catalysts, even in {dependent conduit}s with a block only two cells away.GIG}A glider injection gate. This is a device for {inject}ing a {glider} into a glider {stream}. The injected glider is synthesized from one or more incoming {spaceship}s assisted by the presence of the GIG. (This contrasts with some other glider injection reactions which do not require a GIG, as in {inject}.) Gliders already in the glider stream pass through the GIG without interfering with it. A GIG usually consists of a small number of oscillators. For example, in July 1996 Dieter Leithner found the following reaction which allows the construction of a pseudo-period 14 glider stream. It uses two {LWSS} streams, a {pentadecathlon} and a {volcano}. Glider injection gates are useful for building glider {gun}s with {pseudo}-periods that are of the form nd, where n is a positive integer, and d is a proper divisor of some convenient base gun period (such as 30 or 46), with d > 13.                                                                  glasses$Compare {scrubber} and {spark coil}.p26                   gliderThe smallest, most common and first discovered {spaceship}. This was found by Richard Guy in 1970 while Conway's group was attempting to track the {evolution} of the {R-pentomino}. The name is due in part to the fact that it is {glide symmetric}. (It is often stated that Conway discovered the glider, but he himself has said it was Guy. See also the cryptic reference ("some guy") in {Winning Ways}.) The term "glider" is also occasionally (mis)used to mean "spaceship".c/4 diagonallyp4glider-block cycleAn infinite {oscillator} based on the following reaction (a variant of the {rephaser}). The oscillator consists of copies of this reaction displaced 2n spaces from one another (for some n>6) with blocks added between the copies in order to cause the reaction to occur again halfway through the period. The period of the resulting infinite oscillator is 8n-20. (Alternatively, in a cylindrical universe of width 2n the oscillator just consists of two gliders and two blocks.)glider constructibleSee {glider synthesis}.glider construction= {glider synthesis}.glider duplicatorAny reaction in which one input {glider} is converted into two output gliders. This can be done by {oscillator}s or {spaceship}s, or by {Herschel conduit}s or other {signal} {circuit}ry such as the {stable} example shown under {splitter}. The most useful glider duplicators are those with low {period}s. The following period 30 glider duplicator demonstrates a simple mechanism found by Dieter Leithner. The input glider stream comes in from the upper left, and the output glider streams leave at the upper and lower right. One of the output glider streams is inverted, so an {inverting reflector} is required to complete the duplicator. To produce non-parallel output, an {inline inverter} could be substituted for the northmost p30 glider gun. Spaceship {convoy}s that can duplicate gliders are very useful since they (along with {glider turner}s) provide a means to clean up many dirty puffers by duplicating and turning output gliders so as to impact into the {exhaust} to clean it up. Glider duplicators and turners are known for backward gliders using p2 c/2 spaceships, and for forward gliders using p3 c/3 spaceships. These are the most general duplicators for these speeds.k %& %& "#*./!"#)-/"#*+,-.%&+,-%&            ! """#0 glider gun~A {gun} that fires {glider}s. For examples, see {Gosper glider gun}, {Simkin glider gun}, {new gun}, {p45 gun}. True-period glider guns are known for some low periods, and for all periods over 53 using {Herschel conduit} {technology}. See {true} for a list of known true-period guns. The lowest true-period gun possible is the {p14 gun} since that is the lowest possible period for any glider {stream}, but no example has yet been found. Pseudo-period glider guns are known for every period above 13. These are made by using multiple true-period guns of some multiple of the period, and glider {inject}ion methods to fill in the gaps.glider injection gate= {GIG} glider lane See {lane}. gliderlessA {gun} is said to be gliderless if it does not use {glider}s. The purist definition would insist that a glider does not appear anywhere, even incidentally. For a long time the only known way to construct {LWSS}, {MWSS} and {HWSS} guns involved gliders, and it was not until April 1996 that Dieter Leithner constructed the first gliderless gun (a p46 LWSS gun). In October 2017 Matthias Merzenich used two copies of {Tanner's p46} to create a p46 MWSS gun. This is the smallest known gliderless gun, and also the smallest known MWSS gun.{                              #$#$    $%$%&''( glider pairTwo gliders travelling in the same direction with a specific spacetime offset. In a {transceiver} the preferred term is {tandem glider}. For several years, glider pairs on {lane}s separated by 9 or 10 {half diagonal}s were the standard building blocks in {Geminoid} {construction arm} {recipe}s. In more recent 0hd and {single-channel} construction toolkits, all gliders share the same lane, but glider pairs and {singleton}s are still important concepts.glider-producing switch engineSee {stabilized switch engine}. glider pushervAn arrangement of a {queen bee shuttle} and a {pentadecathlon} that can push the path of a passing glider out by one half-diagonal space. This was found by Dieter Leithner in December 1993 and is shown below. It is useful for constructing complex {gun}s where it may be necessary to produce a number of gliders travelling on close parallel paths. See also {edge shooter}.'               glider recipe= {glider synthesis}.glider reflectorSee {reflector}.gliders by the dozenuIn early references this is usually shown in a larger form whose generation 1 is generation 8 of the form shown here.stabilizes at time 184glider stopperA {Spartan} logic circuit discovered by Paul Callahan in 1996. It allows a {glider} signal to pass through the circuit, leaving behind a beehive that can cleanly absorb a single glider from a perpendicular glider {stream}. Two optional glider outputs are also shown. The circuit can't be re-used until the beehive "bit" is cleared by the passage of at least one perpendicular input. A similar mechanism discovered more recently is shown in the {beehive stopper} entry.2#""#$  !      +, + )+)*!!""#$$-%glider synthesisfConstruction of an object by means of {glider} collisions. It is generally assumed that the gliders should be arranged so that they could come from infinity. That is, gliders should not have had to pass through one another to achieve the initial arrangement. Glider syntheses for all {still life}s and known {oscillator}s with at most 14 cells were found by Dave Buckingham. As of June 2018, this limit has been increased to 18 cells. Perhaps the most interesting glider syntheses are those of {spaceship}s, because these can be used to create corresponding {gun}s and {rake}s. Many of the c/2 spaceships that are based on {standard spaceship}s have been synthesized, mostly by Mark Niemiec. In June 1998 Stephen Silver found syntheses for some of the {Cordership}s (although it was not until July 1999 that Jason Summers used this to build a Cordership gun). In May 2000, Noam Elkies suggested that a 2c/5 spaceship found by Tim Coe in May 1996 might be a candidate for glider synthesis. Initial attempts to construct a synthesis for this spaceship got fairly close, but it was only in March 2003 that Summers and Elkies managed to find a way to perform the crucial last step. Summers then used the new synthesis to build a c/2 forward rake for the 2c/5 spaceship; this was the first example in Life of a rake which fires spaceships that travel in the same direction as the rake but more slowly. A 3-glider synthesis of a {pentadecathlon} is shown in the diagram below. This was found in April 1997 by Heinrich Koenig and came as a surprise, as it was widely assumed that anything using just three gliders would already be known.  glider to 2 blocks]A {converter} discovered by Sergei Petrov on 8 October 2011, used in his later {G4 receiver}.                 glider to blockA {converter} discovered by Sergei Petrov that places a block at its right edge in response to a single {glider} input. This has a variety of uses in {Herschel circuit}ry and other {signal}-processing applications.#             glider trainA certain p64 c/2 orthogonal {puffer} that produces two rows of {block}s and two backward {glider} waves. Ten of these were used to make the first {breeder}.\%&'()*$**$)&'% $ # $ ( ) # % ) * $ ( ) (($()#%)*#$()$%&'$)*$*%&'()*+ glider turnerAny reaction in which a {glider} is turned onto a new path by a {spaceship}, {oscillator}, or {still life} {constellation}. In the last two cases, the glider turner is usually called a {reflector} if the reaction is repeatable, or a {one-time} {turner} if the reaction can only happen once. Glider turners are easily built using {standard spaceship}s. The following diagram shows a convoy which turns a {forward glider} 90 degrees, with the new glider also moving forwards. Small rearrangements of the back two spaceships can alternatively send the output glider into any of the other three directions. See also {glider duplicator} and {reflector}./                        glide symmetricrUndergoing simultaneous reflection and translation. A glide symmetric {spaceship} is sometimes called a {flipper}.GnAn abbreviation specific to {converter}s that produce multiple {glider}s. A "G" followed by any integer value means that the converter produces a {tandem glider} - two parallel glider outputs with lanes separated by the specified number of {half diagonal}s.gnome= {fox}GoE= {Garden of Eden}GoL= {Game of Life}GollyA cross-platform open source Life program by Andrew Trevorrow and Tomas Rokicki. Unlike most Life programs it includes the ability to run patterns using the {hashlife} algorithm. It is available from {http://golly.sourceforge.net}.Gosper glider gunThe first known {gun}, and indeed the first known finite pattern displaying {infinite growth}, found by Bill Gosper in November 1970. This period 30 gun remains the smallest known gun in terms of its bounding box, though some variants of the p120 {Simkin glider gun} have a lower population. Gosper later constructed several other guns, such as {new gun} and the p144 gun shown under {factory}. See also {p30 gun}.$  "# "#      $ Gotts dotsA 41-cell 187x39 {superlinear growth} pattern found by Bill Gosper in March 2006, who named it in honour of Nick Gotts, discoverer of many other low-population superlinear patterns, such as {Jaws}, the {mosquito}es, {teeth}, {catacryst} and {metacatacryst}. See {switch-engine ping-pong} for the lowest-population {superlinear growth} pattern as of July 2018, along with a list of the record-holders. Collisions within the pattern cause it to sprout its Nth {switch engine} at generation T = ~224n-6. The population of the pattern at time t is asymptotically proportional to t times log(t), so the growth rate is O(t ln(t)), faster than {linear growth} but slower than {quadratic growth}.gourmetTFound by Dave Buckingham in March 1978. Compare with {pi portraitor} and {popover}.p32C                           gp= {glider pair}GPSE"= {glider-producing switch engine}grammar^A set of rules for connecting {component}s together to make an object such as a {spaceship}, {oscillator} or {still life}. For example, in August 1989 Dean Hickerson found a grammar for constructing an infinite number of short wide c/3 period 3 spaceships, using 33 different components and a table showing the ways that they can be joined together. grandfather= {grandparent}grandfatherlessA traditional name for a pattern with one or more {parent}s but no grandparent. This was a hypothetical designation until May 2016. See {grandparent} for details. grandparentA pattern is said to be a grandparent of the pattern it gives rise to after two generations. For over thirty years, a well-known open problem was the question of whether any pattern existed that had a parent but no grandparent. In 1972, {LifeLine} Volume 6 mentioned John Conway's offer of a $50 prize for a solution to the problem, but it remained open until May 2016 when a user with the conwaylife.com forum handle 'mtve' posted an example. Other patterns have since been found that have a grandparent but no great-grandparent, or a great-grandparent but no great-great-grandparent. Further examples in this series almost certainly exist, but as of July 2018 none have yet been found. Gray counterFound in 1971. If you look at this in the right way you will see that it cycles through the Gray codes from 0 to 3. Compare with {R2D2}.p4     gray ship = {grey ship} great on-offp2 grey counterM= {Gray counter} (This form is erroneous, as Gray is surname, not a colour.) grey shipA {spaceship} that contains a region with an average density of 1/2, and which is {extensible} in such a way that the region of average density 1/2 can be made larger than any given square region. See also {with-the-grain grey ship}, {against-the-grain grey ship} and {hybrid grey ship}.grinwThe following common {parent} of the {block}. This name relates to the infamous {Cheshire cat}. See also {pre-block}.grow-by-one objectA pattern whose population increases by one cell every generation. The smallest known grow-by-one object is the following 44-cell pattern (David Bell's one-cell improvement of a pattern found by Nicolay Beluchenko, September 2005).,                         growing/shrinking line shipeA {line ship} in which the line repeatedly grows and shrinks, resulting in a high-period {spaceship}.growing spaceship[An object that moves like a {spaceship}, except that its front part moves faster than its back part and a {wick} extends between the two. Put another way, a growing spaceship is a {puffer} whose output is burning {clean}ly at a slower rate than the puffer is producing it. Examples include {blinker ship}s, {pi ship}s, and some {wavestretcher}s.G-to-HSA {converter} that takes a {glider} as an input {signal} and produces a {Herschel} output, which can then be used by other {conduit}s. G-to-Hs are frequently used in {stable} logic circuitry. Early examples include {Callahan G-to-H}, {Silver G-to-H}, and {p8 G-to-H} for periodic circuits. A more compact recent example is the {syringe}.gull = {elevener}gunAny stationary pattern that emits {spaceship}s (or {rake}s) forever. For examples see {double-barrelled}, {edge shooter}, {factory}, {gliderless}, {Gosper glider gun}, {Simkin glider gun}, {new gun} and {true}.gunstarAny of a series of glider {gun}s of period 144+72n (for all non-negative integers n) constructed by Dave Buckingham in 1990 based on his {transparent block reaction} and Robert Wainwright's p72 oscillator (shown under {factory}).gutterqA single straight line of cells along the axis of symmetry of a mirror-{symmetric} pattern. Most commonly this is an orthogonal line, and the pattern is then odd-symmetric (as opposed to even-symmetric, where the axis of symmetry follows the boundary between two rows or columns of cells). The birth rule for Conway's Life trivially implies that if there are no live cells in the gutter of a symmetric pattern, new cells can never be born there. For examples, see {44P5H2V0}, {60P5H2V0}, {Achim's p4}, {brain}, {c/6 spaceship}, {centinal}, {p54 shuttle}, {pufferfish}, {snail}, {spider}, and {pulsar} (in two orientations).half-baked knightshipc/2621440, p2621440) A {self-supporting} {macro-spaceship} with adjustable period but fixed direction, based on the {half-bakery reaction}. This was the first spaceship based on this reaction, constructed in December 2014 by Adam P. Goucher. It moves 6 cells horizontally and 3 cells vertically every 2621440+8N ticks, depending on the relative spacing of the two halves. It is one of the slowest known {knightship}s, and the first one that was not a {Geminoid}. Chris Cain optimized the design a few days later to create the {Parallel HBK}. The spaceship produces gliders from near-diagonal lines of half-bakeries, which collide with each other at 180 degrees. These collisions produce {monochromatic salvo}s that gradually build and trigger {seed}s, which in turn eventually construct small {synchronized} {salvo}s of gliders. These re-activate the lines of half-bakeries, thus closing the cycle and moving the entire spaceship obliquely by (6,3).(6,3 half bakery = {bi-loaf}.half-bakery reaction<The key reaction used in the {half-baked knightship} and {Parallel HBK}, where a half-bakery is moved by (6,3) when a glider collides with it, and the glider continues on a new lane. Ivan Fomichev noticed in May 2014 that pairs of these reactions at the correct relative spacing can create 90-degree output gliders:&          half diagonal&A natural measurement of distance between parallel glider lanes, or between {elbow} locations in a {universal} {construction arm} {elbow operation} library. If two gliders are in the same phase and exactly lined up vertically or horizontally, N cells away from each other, then the two glider {lane}s are considered to be N half diagonals (hd) apart. Gliders that are an integer number of {full diagonal}s apart must be the same colour, whereas integer {half diagonal}s allow for both glider colours. See {colour of a glider}, {linear propagator}. half fleet = {ship-tie}HalfmaxA pattern that acts as a spacefiller in half of the Life plane, found by Jason Summers in May 2005. It expands in three directions at c/2, producing a triangular region that grows to fill half the plane.hammer*To hammer a {LWSS}, {MWSS} or {HWSS} is to smash things into the rear end of it in order to transform it into a different type of {spaceship}. A hammer is the object used to do the hammering. In the following example by Dieter Leithner an LWSS is hammered by two more LWSS to make it into an MWSS.       hammerheadA certain front end for {c/2 spaceship}s. The central part of the hammerhead pattern is supported between two {MWSS}. The picture below shows a small example of a {spaceship} with a hammerhead front end (the front 9 columns).\                                 handCAny object used as a {slow salvo} {target} by a {construction arm}. handshakenAn old MIT name for {lumps of muck}, from the following form (2 generations on from the {stairstep hexomino}): harborKFound by Dave Buckingham in September 1978. The name is by Dean Hickerson.p5@                              harvesterFound by David Poyner, this was the first published example of a {fuse}. The name refers to the fact that it produces debris in the form of {block}s which contain the same number of cells as the fuse has burnt up. c p4 fuse               hashlifefA Life algorithm by Bill Gosper that is designed to take advantage of the considerable amount of repetitive behaviour in many large patterns of interest. It provides a means of evolving repetitive patterns millions (or even billions or trillions) of generations further than normal Life algorithms can manage in a reasonable amount of time. The hashlife algorithm is described by Gosper in his paper listed in the bibliography at the end of this lexicon. Roughly speaking, the idea is to store subpatterns in a hash table so that the results of their {evolution} do not need to be recomputed if they arise again at some other place or time in the evolution of the full pattern. This does, however, mean that complex patterns can require substantial amounts of memory. Tomas Rokicki and Andrew Trevorrow implemented Hashlife into {Golly} in 2005. See also {macrocell}.hassleSee {hassler}.hasslerAn {oscillator} that works by hassling (repeatedly moving or changing) some object. For some examples, see {Jolson}, {baker's dozen}, {toad-flipper}, {toad-sucker} and {traffic circle}. Also see {p24 gun} for a good use of a {traffic light} {hassler}.hat3Found in 1971. See also {twinhat} and {sesquihat}.p1 HBK= {half-baked knightship}hdAbbreviation for {half diagonal}. This metric is used primarily for relative measurements of glider lanes, often in relation to {self-constructing} circuitry; compare {Gn}.heat]For an {oscillator} or {spaceship}, the average number of cells which change state in each generation. For example, the heat of a {glider} is 4, because 2 cells are born and 2 die every generation. For a period n oscillator with an r-cell {rotor} the heat is at least 2r/n and no more than r(1-(n mod 2)/n). For n=2 and n=3 these bounds are equal.heavyweight emulator= {HW emulator}heavyweight spaceship= {HWSS}heavyweight volcano= {HW volcano} hebdarole7Found by Noam Elkies, November 1997. Compare {fumarole}. The smaller version shown below was found soon after by Alan Hensel using a component found by Dave Buckingham in June 1977. The top ten rows can be stabilized by their mirror image (giving an {inductor}) and this was the original form found by Elkies.p7g                                              hectic-Found by Robert Wainwright in September 1984.p30J            %&!%&    %%&&''Heisenburp device<A pattern which can detect the passage of a {glider} without affecting the glider's path or timing. The first such device was constructed by David Bell in December 1992. The term, coined by Bill Gosper, refers to the fact that Heisenberg's Uncertainty Principle fails to apply in the Life universe. See also {stable pseudo-Heisenburp} and {natural Heisenburp}. The following is an example of the kind of reaction used at the heart of a Heisenburp device. The glider at bottom right alters the reaction of the other two gliders without itself being affected in any way.     Heisenburp effectSee {Heisenburp device}.helixA convoy of {standard spaceship}s used in a {Caterpillar} to move some piece of debris at the speed of the Caterpillar. The following diagram illustrates the idea. The leading edge of this example helix, represented by the glider at the upper right in the pattern below, moves at a speed of 65c/213, or slightly faster than c/4. Adjustable-speed helices can produce a very wide range of spaceship speeds; see {Caterloopillar}.  !    !$%&   $ %                    %$%&#$& #$%#$%#$%$%+*+,) * , )!*!+!*"+"))** *(*)***+++++ +'+(+*+ ,,,,,, ,',(,), - - ----- -'-(-)- . . .......(.). / / //////0 0 0 0000111 1 1 111222 2 2333*344)4*4+4(5)5+5(6)6*6)7*7 8 8 89 9 : ;< <-= heptapletAny 7-cell {polyplet}. heptapoleThe {barberpole} of length 7.p2   heptominoAny 7-cell {polyomino}. There are 108 such objects. Those with names in common use are the {B-heptomino}, the {Herschel} and the {pi-heptomino}.HerschelThe following pattern which occurs at generation 20 of the {B-heptomino}. The name is commonly ascribed to the Herschel heptomino's similarity to a planetary symbol. William Herschel discovered Uranus in 1781. However, in point of fact a Herschel bears no particular resemblance to either of the symbols used for Uranus, but does closely resemble the symbol for Saturn. So the appropriate name might actually be "Huygens", but "Herschel" is now universally used by tradition. Herschels are one of the most versatile types of {signal} in stable circuitry. {R-pentomino}es and {B-heptomino}es naturally evolve into Herschels, and {converter}s have also been found that change {pi-heptomino}es and several other signal types into Herschels, and vice versa. See {elementary conduit}.stabilizes at time 128Herschel circuitA series of {Herschel conduit}s or other components, connected by placing them so that the output {Herschel}s from early conduits become the input Herschels for later conduits. Often the initial component is a {converter} accepting some other signal type as input - usually a glider, in which case a {syringe} is most commonly used. The {Silver reflector} is a well-known early {Spartan} Herschel circuit from before the syringe was discovered, where the initial converter is a {Callahan G-to-H}. Sometimes a direct connection between two conduits is not possible due to unwanted gliders that destroy required {catalyst}s, or wanted gliders that are not able to escape. In this case, small "spacer" conduits such as {F116}, {F117}, {Fx77}, {R64}, {L112}, or {L156} can be inserted between the other conduits to solve the problem. Some converter or {factory} conduits do not produce a Herschel as output, instead generating other useful results such as gliders, {boat}s or {MWSS}es. See {Herschel-to-glider}, {demultiplexer}, and {H-to-MWSS} respectively for examples of these. For those conduits which do produce an unwanted Herschel, an {eater} such as {SW-2} can be added to delete it. If the first and last conduits of a chain connect to each other in a loop then there is no need for a syringe to generate the first Herschel, or an eater to consume the last one. The circuit becomes a self-supporting {Herschel loop}. A loop is also formed by a {syringe} connected to a Herschel-to-glider converter, with the glider reflected back to the syringe's input with glider reflectors of the appropriate colour, usually {Snark}s. In either case, if the loop has a surplus {glider} output, it becomes a {gun}; if no output is available it is an {emu}.Herschel climberAny {reburnable fuse} reaction involving {Herschel}s. May refer specifically to the {(23,5)c/79 Herschel climber} used in the {waterbear}, or one of several similar reactions with various velocities. See also {Herschel-pair climber}.Herschel component= {Herschel conduit}Herschel conduitA {conduit} that moves a {Herschel} from one place to another. See also {Herschel loop}. Well over a hundred simple stable Herschel conduits are currently known. As of June 2018 the number is approximately 150, depending on the precise definition of "simple" - e.g., fitting inside a 100x100 bounding box, and producing output in no more than 300 {tick}s. In general a Herschel conduit can be called "simple" if its active reaction does not return to a Herschel stage except at its output. Compare {elementary conduit}, {composite conduit}. A description of common usage in complex circuitry, using {syringe}s and {Snark}s to make compact connections, can be found in {Herschel circuit}. The original {universal} set consisted of sixteen stable Herschel conduits, discovered between 1995 and 1998 by Dave Buckingham (DJB) and Paul Callahan (PBC). These are shown in the following table. In this table, the number in "name/steps" is the number of {tick}s needed to produce an output Herschel from the input Herschel. "m" tells how the Herschel is moved (R = turned right, L = turned left, B = turned back, F = unturned, f = flipped), and "dx" and "dy" give the displacement of the centre cell of the Herschel (assumed to start in the orientation shown above). See also {Herschel transceiver}.)Herschel descendantA common active pattern occurring at generation 22 of a {Herschel}'s {evolution}: There are other evolutionary paths leading to the same pattern, including the modification of a {B-heptomino} implied by generation 21 of a Herschel. Herschel great-grandparenteA specific three-{tick} predecessor of a {Herschel}, commonly seen in {Herschel conduit} collections that contain {dependent conduit}s. In some situations it is helpful to display the input reaction in this form instead of the standard Herschel form. Dependent conduit inputs are catalysed by a {transparent} block before the Herschel's standard form can appear, and before the Herschel's {first natural glider} is produced. This means that these conduits will fail if an actual Herschel is placed in the "correct" input location for a dependent conduit. Refer to {F166} or {Lx200} to see the correct relative placement of the standard transparent block catalyst. Almost all known Herschel conduits produce a Herschel great-grandparent near the end of their evolutionary sequence. In the original {universal} set of Herschel conduits, {Fx158} is the only exception. Herschel loopYA cyclic {Herschel track}. Although no loop of length less than 120 generations has been constructed it is possible to make {oscillator}s of smaller periods by putting more than one Herschel in a higher-period track. In this way oscillators, and in most cases {gun}s, of all periods from 54 onwards can now be constructed (although the p55 case is a bit strange, shooting itself with gliders in order to stabilize itself). A mechanism for a period-52 loop was found in April 2018, but it includes a stage where the signal is carried by a triplet of {glider}s so it may not be considered to be a pure Herschel loop. The missing period, 53, is a difficult case simply because 53 is prime and so no small sparkers or reflectors are available. See {Simkin glider gun} and {p256 gun} for the smallest known Herschel loops. See also {emu} and {omniperiodic}.Herschel-pair climberAny {reburnable fuse} reaction involving pairs of {Herschel}s. May refer specifically to the {31c/240 Herschel-pair climber} used in the {Centipede}, or one of several similar reactions with various velocities. See also {Herschel climber}.Herschel receiverAny {circuit} that converts a {tandem glider} into a {Herschel} {signal}. The following diagram shows a pattern found by Paul Callahan in 1996, as part of the first stable glider {reflector}. Used as a receiver, it converts two parallel input gliders (with path separations of 2, 5, or 6) to an {R-pentomino}. The signal is then converted to a Herschel by one of several known mechanisms, the first of which was found by Dave Buckingham way back in 1972. The second is {elementary conduit} {RF48H}, found by Stephen Silver in October 1997. The receiver version shown below uses Buckingham's R-to-Herschel converter, which is made up of elementary conduit {RF28B} followed by {BFx59H}.:/1&'/0&'0     + & ' + - % ( + ,  & '    ,-,-()(***+  2!Herschel stopper"A method of cleanly suppressing a {Herschel} signal with an {asynchronous} {boat-bit}, discovered by Dean Hickerson. Here a {ghost Herschel} marks the location of the output signal, in cases where the boat-bit is not present. Other boat-bit locations that allow for clean suppression of a Herschel are also known. This term is also sometimes used to refer to any mechanism that cleanly suppresses a Herschel. These usually allow the Herschel's {first natural glider} to escape, so they are more commonly classified as {converter}s. See {SW-2}.?$%$%$%      $   " # $ " "        #$$!"#!&Herschel-to-gliderThe largest category of {elementary conduit}. Gliders are very common and self-supporting, so it's much easier to find these than any other type of output {signal}. A large collection of these H-to-G {converter}s has been compiled, with many different output {lane}s and timings. These can be used to synchronize multiple signals to produce {gun} patterns or complex logic circuitry. See {NW31T120} for an example.Herschel trackZA {track} for {Herschel}s. An equivalent term is {Herschel circuit}. See also {B track}.Herschel transceiverQAn adjustable {Herschel conduit} made up of a {Herschel transmitter} and a {Herschel receiver}. The intermediate stage consists of a {tandem glider} - two {glider}s on parallel {lane}s - so that the transmitter and receiver can be separated by any required distance. The conduit may be {stable}, or may contain low-period {oscillator}s.Herschel transmitterAny {Herschel}-to-two-{glider} {converter} that produces a {tandem glider} that can be used as input to a {Herschel receiver}. If the gliders are far enough apart, and if one of the gliders is used only for cleanup, then the transmitter is {ambidextrous}: with a small modification to the receiver, a suitably oriented mirror image of the receiver will also work. The following diagram shows a {stable} Herschel transmitter found by Paul Callahan in May 1997: Examples of small reversible p6 and p7 transmitters are also known, and more recently several alternate {Herschel transceiver}s have been found with different lane spacing, e.g., 0, 2, 4, 6, and 13.!        Hertz oscillatorKCompare {negentropy}, and also {cauldron}. Found by Conway's group in 1970.p8#          hexadecimal= {beehive and dock}hexapletAny 6-cell {polyplet}.hexapoleThe {barberpole} of length 6.p2  hexominoAny 6-cell {polyomino}. There are 35 such objects. For some examples see {century}, {stairstep hexomino}, {table}, {toad} and {Z-hexomino}.HF= {honey farm}HFx58BA common {Herschel} to {B-heptomino} converter, used as the first stage of {F117} and many other Herschel conduits. There are two variants, both shown in the pattern below.J )   '() &  &'2320201         1 /1/01#$/#$'('()**4 H-heptominooName given by Conway to the following {heptomino}. After one generation this is the same as the {I-heptomino}.high-bandwidth telegraph,A variant of the {telegraph} constructed by Louis-Francois Handfield in February 2017, using periodic components to achieve a transmission rate of one bit per 192 ticks. The same ten signals are sent as in the original {telegraph} and the {p1 telegraph}, but information is encoded more efficiently in the timing of those signals. Specifically, the new transmitter sends five bits every 960 ticks by adjusting the relative timings inside each of the five mirror-image paired subunits of the composite signal in the beehive-chain {lightspeed wire} {fuse}.p960 p30 circuitryhigh-clearanceSee {clearance}.highway robber'Any mechanism that can retrieve a signal from a spaceship {lane} while allowing spaceships on nearby lanes to pass by unaffected. In practice the spaceship is generally a glider. The signal is removed from the lane, an output signal is generated elsewhere, and the highway robber returns to its original state. A competent highway robber does not affect gliders even on the lane adjacent to the affected glider stream, except during its recovery period. A perfect highway robber doesn't affect later gliders even in the lane to which it is attached, even during its recovery period. Below is a near-perfect highway robber "bait" that requires three {synchronized} signals to rebuild (the {Herschel}, {B-heptomino}, and {glider}.) The glider at the top right passes by unharmed, but another glider following on the same {lane} 200 ticks later will be cleanly reflected to a new path, and another glider following that one will also pass by unharmed. The only imperfection is a few ticks at the very end of the reconstruction, as the beehive is being rebuilt:a" "  !"            !! &&&(&)& ' ' '''(')' ( (( )) )")*)*!*"*)***+*(+)+++--..//0033444455,6hive = {beehive} hivenudger}A {spaceship} found by Hartmut Holzwart in July 1992. (The name is due to Bill Gosper.) It consists of a {pre-beehive} escorted by four {LWSS}. In fact any LWSS can be replaced by a {MWSS} or an {HWSS}, so that there are 45 different single-hive hivenudgers. Wider versions can be made by stabilizing the front of the extended "pre-beehive", as in the {line puffer} shown below.c/2 orthogonallyp4*              honey bitA block and pond {constellation} used in the {OTCA metapixel} by Brice Due in 2006, to store and retrieve a bit of data - specifically, the presence or absence of a neighbor {metacell}. The "0" state of the honey bit memory unit is a simple {beehive}, which is also the source of the name. An input glider collides with the beehive to convert it into the honey bit constellation, which can be thought of as a value of "1" stored in the memory unit. A passing LWSS can then test for the presence of the pond. If a collision occurs, the LWSS and the honey bit constellation are mutually annihilated, leaving just the original beehive. Below is the honeybit constellation with the two reactions occurring in the opposite order - test, then reset. If the pond is not present, the LWSS passes by the beehive without affecting it. Thus a test input has an output for the "0" case, but not for the "1" case. For an alternative memory-unit mechanism with both "0" and "1" outputs, see {demultiplexer}. The honey bit is also an interesting {eater} for the {HWSS} as shown below. An HWSS colliding with the pond happens to create the exact same reset glider used in the above memory unit.          honeycombp1  honey farm$A common formation of four beehives.p1            hookAnother term for a {bookend}. It is also used for other hook-shaped things, such as occur in the {eater1} and the {hook with tail}, for example.hook with tailFor a long time this was the smallest {still life} without a well-established name. It is now a vital component of the smallest known {HWSS} {gun}, where it acts as a {rock}.p1houndstooth agarLThe p2 {agar} that results from tiling the plane with the following pattern.housesThe following {induction coil}. It is generation 3 of the {pi-heptomino}. See {spark coil} and {dead spark coil}. H-to-G#A {Herschel-to-glider} {converter}. H-to-MWSSWA {Spartan} {converter} found by Tanner Jacobi in October 2015, which converts an input {Herschel} to a middleweight spaceship. The key discovery was a very small but slightly {dirty} H-to-MWSS conduit, where a Herschel is catalyzed to produce an {MWSS} but also leaves behind a beehive. Prefixing two {R64} conduits to this produces a {composite} converter that successfully deletes the beehive in advance, using the input Herschel's {first natural glider}. There are many other ways to remove the beehive using a spare glider or additional conduits, but they are generally less compact than this.T$%$%"#"#()()    !"  -. - . !!!!!"""""""##$($)$(%)%&&,&-&','-'(()**&*'*+++&+'+/,hustler&Found by Robert Wainwright, June 1971.p3       hustler IIp4*              HW emulator>Found by Robert Wainwright in June 1980. See also {emulator}.p4"           HWSSA heavyweight spaceship, the fourth most common {spaceship}. Found by Conway in 1970 by modifying a {LWSS}. See also {MWSS}. The HWSS possesses both a {tail spark} and a {domino} {belly spark} which can easily perturb other objects as it passes by. The spaceship can also perturb some objects in additional ways. For examples, see {puffer} and {glider turner}. Dave Buckingham found that the HWSS can be synthesized using three gliders as shown below:c/2 orthogonallyp4  HWSS emulator= {HW emulator} HW volcano_A p5 {domino} {sparker}, found by Dean Hickerson in February 1995. At least four progressively smaller forms of this sparker have been found, including a 25-cell-wide version found by David Eppstein in 2003, and a vertically narrower 28-cell-wide version by Karel Suhajda in 2004. Scot Ellison's 17-cell-wide version is shown in the {zweiback} entry.p5                                                           " #        "     "   !    $hybrid grey shipA {grey ship} containing more than one type of region of density 1/2, usually a combination of a {with-the-grain grey ship} and an {against-the-grain grey ship}. I-heptominooName given by Conway to the following {heptomino}. After one generation this is the same as the {H-heptomino}.IMG= {intermitting glider gun} ImmigrationA form of {colourised Life} in which there are two types of ON cell, a newly-born cell taking the type of the majority of its three {parent cells} and surviving cells remaining of the same type as in the previous generation.independent conduitsA {Herschel conduit} in which the input Herschel produces its {first natural glider}. Compare {dependent conduit}.induction coilAny object used to stabilize an edge (or edges) without touching. The tubs used in the {Gray counter} are examples, as are the blocks and snakes used in the {Hertz oscillator} and the heptomino at the bottom of the {mathematician}.inductorAny {oscillator} with a row of dead cells down the middle and whose two halves are mirror images of one another, both halves being required for the oscillator to work. The classic examples are the {pulsar} and the {tumbler}. If still lifes are considered as p1 oscillators then there are numerous simple examples that include this kind of central {gutter}, such as {table on table}, {dead spark coil} and {cis-mirrored R-bee}. Some spaceships, such as the {brain}, the {snail} and the {spider}, use the same principle.infinite glider hotel/A pattern by David Bell, named after Hilbert's "infinite hotel" scenario in which a hotel with an infinite number of rooms has room for more guests even if it is already full, simply by shuffling the old guests around. In this pattern, two pairs of {Cordership}s moving at c/12 are pulling apart such that there is an ever-lengthening {glider} track between them. Every 128 generations another glider is {inject}ed into the glider track (see {LWSS-glider bounce}), joining the gliders already circulating there. The number of gliders in the track therefore increases without limit. The tricky part of this construction is that even though all the previously injected gliders are repeatedly flying through the injection point, that point is guaranteed to be empty when it is time for the next glider to be injected.infinite growth Growth of a finite pattern such that the {population} tends to infinity, or at least is unbounded. Sometimes the term is used for growth of something other than population (for example, length), but here we will only consider infinite population growth. The first known pattern with infinite growth in this sense was the {Gosper glider gun}, created in a response to a $50 prize challenge by John Conway. Martin Gardner's October 1970 article described the challenge as "Conway conjectures that no pattern can grow without limit", but Conway later explained that he had always expected that this would be disproved. The original purpose in investigating CA rules including B3/S23 was to show that a very simple two-state rule could support a {universal computer} and/or {universal constructor}. If all finite patterns could be proven to be bounded, neither of these would be possible. An interesting question is: What is the minimum population of a pattern that exhibits infinite growth? In 1971 Charles Corderman found that a {switch engine} could be stabilized by a {pre-block} in a number of different ways, giving 11-cell patterns with infinite growth. This record stood for more than quarter of a century until Paul Callahan found, in November 1997, two 10-cell patterns with infinite growth. The following month he found the one shown below, which is much neater, being a single {cluster}. This produces a stabilized switch engine of the block-laying type. Nick Gotts and Paul Callahan showed in October 1997 that there is no infinite growth pattern with fewer than 10 cells, so that question has now been answered. In October 2014, Michael Simkin discovered a three-glider collision that produces a glider-producing {stabilized switch engine} and thus produces infinite growth from the smallest possible number of gliders (since all 71 {2-glider collision}s have a finite limit population). Also of interest is the following pattern (again found by Callahan), which is the only 5x5 pattern with infinite growth. This too emits a block-laying switch engine. Following a conjecture of Nick Gotts, Stephen Silver produced, in May 1998, a pattern of width 1 which exhibits infinite growth. This pattern was very large (12470x1 in the first version, reduced to 5447x1 the following day). In October 1998 Paul Callahan did an exhaustive search, finding the smallest example, the 39x1 pattern shown below. This produces two block-laying switch engines, stability being achieved at generation 1483. Larger patterns have since been constructed that display {quadratic growth}. Although the simplest infinite growth patterns grow at a rate that is (asymptotically) linear, many other types of growth rate are possible, {quadratic growth} (see also {breeder}) being the fastest. Dean Hickerson has found many patterns with unusual growth rates, such as {sawtooth}s and a {caber tosser}. Another pattern with superlinear but non-quadratic growth is {Gotts dots}. See also {Fermat prime calculator}. initials = {monogram}injectA reaction in which a hole in a regular spaceship stream is filled partially or fully by adding a new spaceship of the same type without affecting the existing spaceships in the stream. Depending on the period of the stream, different mechanisms can be used. For adding a spaceship to an existing multi-lane {convoy}, see {inserter}. For large period glider streams, simple reactions such as {LWSS-LWSS bounce} and {LWSS-glider bounce} suffice. If {Herschel} technology is used, a large number of {edge shooter}s and {transparent} conduits are known. Simple examples include the {NW31} {Herschel-to-glider} {converter} and the {Fx119 inserter}. Shown below is an injector found by Dave Buckingham that can fill a hole in a p15 glider stream: For very low-period glider streams, a {GIG} is a much more efficient insertion method, in the sense that fewer {synchronized} {signal}s are needed. However, it has been shown that colliding gliders can complete an insertion even into a single-glider gap in a period-14 stream.            inline inverterThe following reaction in which a p30 {gun} can be used to invert the presence or absence of gliders in a p30 stream, with the output glider stream being in the same direction as the input glider stream.0   "#  "#             $ inserterA mechanism that can add another spaceship into a stream or convoy of other spaceships without affecting the existing spaceships. For examples see {Fx119 inserter}, {tee}, {GIG}, {clock insertion} and {inject}.integral= {integral sign} integral signp1  intentionless = {elevener} interchange#A common formation of six blinkers.p2       intermediate targetA temporary product of a partial {slow salvo}, {elbow operation}, or {glider synthesis}. An intermediate target is a useful step toward a desired outcome, but will not appear in the final construction.intermittent streamA {stream} of spaceships which is based on a periodic stream, but which can contain holes where some of the spaceships are not present. There is a base period for the intermittent stream such that if a spaceship arrives at a specific location, then it always does so at a generation which is a multiple of the base period. For example, the output from a period 30 glider gun where every third glider is deleted is an intermittent stream. A {pseudo-random glider generator} can produce a complicated intermittent stream with no obvious pattern. Intermittent streams can be used to transmit {signal}s, where holes in the stream can also convey information. For example, the stream can be processed by an {inverter} having the same period.intermitting glider gunDespite the name, an intermitting glider gun (IMG) is more often an {oscillator} than a {gun}. There are two basic types. A type 1 IMG consists of two guns firing at one another in such a way that each gun is temporarily disabled on being hit by a glider from the other gun. A type 2 IMG consists of a single gun firing at a 180-degree glider {reflector} in such a way that returning gliders temporarily disable the gun. Both types of IMG can be used to make glider guns of periods that are multiples of the base period. This is done by firing another gun across the two-way {intermittent stream} of gliders in the IMG in such a way that gliders only occasionally escape.inverterjA device which can be used to invert the presence or absence of spaceships in an {intermittent stream} of spaceships. The device must be a gun whose period matches the base period of the stream, since if there are no input spaceships then the device must produce spaceships as the result of the inversion. Typically the spaceships are gliders, and the inverter is made from a glider gun. Inverters provide a way to produce a NOT logic operation on a stream. There are several ways to produce an inverter. The simplest method is to simply hit the output of a gun with the input stream to delete its spaceships, producing an output stream that is always turned 90 degrees from the input stream. An example is the northernmost p30 gun in the {glider duplicator} example pattern. For one way to produce an inverted output stream which is not turned, see {inline inverter}.inverting reflectorSee {inverter}.islandThe individual {polyplet}s of which a {stable} pattern consists are sometimes called islands. So, for example, a {boat} has only one island, while an {aircraft carrier} has two, a {honey farm} has four and the standard form of the {eater3} has five.Iwona!The following {methuselah} found by Andrzej Okrasinski in August 2004. It has a final population of 3091 and covers an area of 413 by 364 cells, not counting the 47 gliders it produces. Its {ash} consists of typical stable objects and blinkers, along with the relatively rare {paperclip}.stabilizes at time 28786       J = {Herschel}jack'Found by Robert Wainwright, April 1984.p4*               jagged linesA pattern constructed by Dean Hickerson in May 2005 that uses {puffer}s to produce a line of {bi-block}s that weaves back and forth in a complicated way.jam3Found by Achim Flammenkamp in 1988, but not widely known about until its independent discovery (and naming) by Dean Hickerson in September 1989. Compare with {mold}. In fact this is really very like {caterer}. In terms of its 7x7 {bounding box} it ties with {trice tongs} as the smallest p3 {oscillator}.p3 JavaLifeSearchSee {lifesrc}.Jaws|A {breeder} constructed by Nick Gotts in February 1997. In the original version Jaws had an initial {population} of 150, which at the time was the smallest for any known pattern with {superlinear growth}. In November 1997 Gotts produced a 130-cell Jaws using some {switch engine} {predecessor}s found by Paul Callahan. See {switch-engine ping-pong} for the lowest-population superlinear growth pattern as of July 2018, along with a list of the record-holders. Jaws consists of eight pairs of switch engines which produce a new block-laying switch engine (plus masses of junk) every 10752 generations. It is therefore an MMS breeder.JC= {dead spark coil}JHC6John Horton Conway. Also another name for {monogram}. J-heptomino = {Herschel}JLS= {JavaLifeSearch}JolsonTwo {block}s {hassle}d by two {pentadecathlon}s. Found by Robert Wainwright in November 1984 and named by Bill Gosper. A p9 version using {snacker}s instead of pentadecathlons is also possible.p15E                             junk= {ash}.JustynaCThe following {methuselah} found by Andrzej Okrasinski in May 2004.stabilizes at time 26458    Karel's p15An {oscillator} discovered by Karel Suhajda on December 11, 2002. It consists of a period 15 rotor supported by the domino spark of a pentadecathlon. It provides accessible sparks that can be used to perturb reactions or thin signal {stream}s.p15         keeper@A type of {factory} {circuit} that always results in the presence of an object in the output location, whether or not the object was previously present. In many cases it is easy to construct examples by connecting multiple circuits to shoot down an object with a {glider}, then rebuild the object again later. The smallest keeper circuits accomplish the same thing more directly with a lucky preliminary {spark} from the active reaction, which removes the existing object (if any) just before the construction occurs. Below is a useful block keeper with a {Herschel} input.1 !  !     -.  -.      !""" " "# # #/$keys-See {short keys}, {bent keys} and {odd keys}.kickback/= {kickback reaction} or {180-degree kickback}.kickback reactionQThe following collision of two {glider}s whose product is a single glider travelling in the opposite direction to one of the original gliders. This is important in the proof of the existence of a {universal constructor}, and in Bill Gosper's {total aperiodic}, as well as a number of other constructions. See also {180-degree kickback}. kidney0A Gosperism for {century}. See also {diuresis}. killer toadsA pair of {toad}s acting together so that they can eat things. Here, for example, are some killer toads eating an {HWSS}. Similarly they can eat a {MWSS} (but not a {LWSS}). For another example see {twirling T-tetsons II}. See also {candlefrobra}.           Klein bottleAs an alternative to a {torus}, it's possible to make a finite Life universe in the form of a Klein bottle. The simplest way to do this is to use an m x n rectangle with the top edge joined to the bottom edge (as for a torus) and the left edge twisted and joined to the right. knightshipAny {spaceship} of type (2m,m)/n - that is, a spaceship of any speed that moves obliquely in a (2,1) direction. The first Conway's Life knightship was a variant of Andrew Wade's {Gemini} spaceship, constructed in May 2010. The next was an even slower knightship based on the {half-bakery reaction}. A knightship must be asymmetric and its period must be at least 6. This is barely within the range of current {search program}s, as proven by the discovery on March 6, 2018 of an {elementary} knightship, {Sir Robin}, by Adam P. Goucher and Tomas Rokicki. By analogy with the corresponding fairy chess pieces, spaceships of types (3m,m)/n, (3m,2m)/n and (4m,m)/n would presumably be called camelships, zebraships and giraffeships, respectively. Such spaceships do exist (see {universal constructor}) but small elementary versions are even more difficult to search for. Any of these ship types could be constructed by trivially modifying a Gemini spaceship, or less trivially by reprogramming one of the more recent small {Geminoid} {construction arm}s, but as of July 2018 a camelship Gemini is the only example that has been explicitly built. Alternatively, the term "knightship" is regularly used to refer to any {oblique} spaceship, such as the original {Gemini} or the {waterbear}. Kok's galaxyAn {oscillator} found by Jan Kok in 1971, currently serving as the icon for {Golly}. See {converter} for a use of this {sparker}.p80 L112A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in July 1996. It is made up of two {elementary conduit}s, HLx53B + {BFx59H}. After 112 ticks, it produces a {Herschel} turned 90 degrees counterclockwise at (12, -33) relative to the input. Its {recovery time} is 61 ticks; this can be reduced slightly by removing the output glider, either with a specialized eater (as in the original {true} p59 gun), or with a {sparker} as in most of the {Quetzal} guns. It can be made {Spartan} by replacing the {aircraft carrier} with an {eater1}. A {ghost Herschel} in the pattern below marks the output location:0    !!"""#%%&&&&''())*L156A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in August 1996. It is made up of three {elementary conduit}s, HLx69R + {RF28B} + {BFx59H}. After 156 ticks, it produces a {Herschel} turned 90 degrees counterclockwise at (17, -41) relative to the input. Its {recovery time} is 62 ticks. It can be made {Spartan} by replacing the {snake} with an {eater1} in one of two orientations. Additional gliders can be produced by removing the southeasternmost eater, or by replacing the RF28B elementary conduit by an alternate version. A {ghost Herschel} in the pattern below marks the output location:>              !!!((())))****+++++,---./lakeAny still life consisting of a simple closed curve made from diagonally connected {domino}es. The smallest example is the {pond}, and the next smallest is this (to which the term is sometimes restricted):p1    laneA path traveled by a glider, or less commonly a spaceship such as a loafer. The lane is centered on the line of symmetry (if any) of the spaceship in question. If a lane is clear, then the spaceship can travel along it without colliding or interfering with any other objects. Diagonal lanes are often numbered consecutively, in half-diagonals ({hd}). Occasionally diagonal lane measurements are given in quarter-diagonals ({qd}), in part because diagonally symmetric spaceships have a line of symmetry 1qd away from the lines available for gliders. It's also convenient that moving a glider forward by 100qd (for example) has the same effect as evolving the same glider for 100 ticks.Laputa)Found by Rich Schroeppel, September 1992.p2       large prime oscillatorAny oscillator with a relatively small {bounding box} whose period is a very large prime. (If the bounding-box restriction is removed, then eight gliders travelling in a four-{Snark} loop would provide a trivial example for any chosen prime.) The first such oscillator was built by Gabriel Nivasch in 2003. The current record holder is an oscillator constructed by Adam P. Goucher with a period that is a Mersenne prime with 13,395 digits (2^44497-1). The next higher Mersenne-prime oscillator, period 2^86243-1, could be constructed with {quadri-Snark}s and {semi-Snark}s. It would actually be significantly smaller than the current record holder. As of June 2018 the construction of this pattern has not yet been completed.large S = {big S}LidkaA {methuselah} found by Andrzej Okrasinski in July 2005. The following variant, pointed out by David Bell, has two fewer cells and lasts two generations longer.stabilizes at time 29053      LifeA 2-dimensional 2-state {cellular automaton} discovered by John Conway in 1970. The states are referred to as ON and OFF (or live and dead). The transition rule is as follows: a cell that is ON will remain ON in the next generation if and only if exactly 2 or 3 of the 8 adjacent cells are also ON, and a cell that is OFF will turn ON if and only if exactly 3 of the 8 adjacent cells are ON. (This is more succinctly stated as: "If 2 of your 8 nearest neighbours are ON, don't change. If 3 are ON, turn ON. Otherwise, turn OFF.")Life32xA freeware Life program by Johan Bontes for Microsoft Windows 95/98/ME/NT/2000/XP: {https://github.com/JBontes/Life32/}. LifeHistoryeA multistate CA rule supported by {Golly}, equivalent to two-state B3/S23 Life but with several additional states intended for annotation purposes. A "history" state records whether an off cell has ever turned on in the past, and other states allow on and off cells to be permanently or temporarily marked, without affecting the {evolution} of the pattern.LifeLabyA shareware Life program by Andrew Trevorrow for the Macintosh (MacOS 8.6 or later): {http://www.trevorrow.com/lifelab/}.LifeLineA newsletter edited by Robert Wainwright from 1971 to 1973. During this period it was the main forum for discussions about Life. The newsletter was nominally quarterly, but the actual dates of its eleven issues were as follows: Lifenthusiast5A Life enthusiast. Term coined by Robert Wainwright.lifesrcDavid Bell's Life {search program} for finding new {spaceship}s and {oscillator}s. This is a C implementation of an algorithm developed by Dean Hickerson in 6502 assembler. Although lifesrc itself is a command-line program, Jason Summers has made a GUI version called {WinLifeSearch} for Microsoft Windows. A Java version, {JavaLifeSearch}, was written in November 2012 by Karel Suhajda. The lifesrc algorithm is only useful for very small periods, as the amount of computing power required rises rapidly with increasing period. For most purposes, period 7 is the practical limit with current hardware. Lifesrc is available from {http://tip.net.au/~dbell/} (source code only). Compare {gfind}. LifeViewer|A scriptable Javascript Life pattern viewer written by Chris Rowett, used primarily on the conwaylife.com discussion forums. light bulbYFound in 1971. The same {rotor} can be embedded in a slightly smaller {stator} like this:p2 lightspeed bubble!A type of {negative spaceship} travelling through the {zebra stripes} agar. The center of the bubble is simple empty space, and the length and/or width of the bubble can usually be extended to any desired size. Below is a small stabilized section of agar containing a sample lightspeed bubble, found by Gabriel Nivasch in August 1999. The bubble travels to the left at the {speed of light}, so it will eventually reach the edge of any finite patch and destroy itself and its supporting agar. An open problem related to lightspeed bubbles was whether large extensible empty areas could be created whose length was not proportional to the width (as it must be in the above case, due to the tapering back edge). This was solved in February 2017 by Arie Paap; a simple period-2 solution is shown below.N "%(+.147:      !"#$%&'()*+,-./0123456789:;<=      !"#$%&'()*+,-./0123456789:;<#      %&'()*+,-./0123456789:;<$=      !"#$%&'()*+,-./0123456789:;<         ! " # $ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < ! & =         ! " ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < ! ' ,         ! " ' ( - . / 0 1 2 3 4 5 6 7 8 9 : ; < !'-2=     !"'(-.3456789:;<!'-38     !"'(-.349:;<!'-39=     !"'(-.349:;<!'-38     !"'(-.3456789:;<!'-2=     !"'(-./0123456789:;<!',     !"'()*+,-./0123456789:;<!&=     !"#$%&'()*+,-./0123456789:;<       !"#$%&'()*+,-./0123456789:;<$=      %&'()*+,-./0123456789:;<       # !!!!!!!! ! ! ! ! !!!!!!!!!!!!! !!!"!#!$!%!&!'!(!)!*!+!,!-!.!/!0!1!2!3!4!5!6!7!8!9!:!;!<!="######## # # # # ################### #!#"###$#%#&#'#(#)#*#+#,#-#.#/#0#1#2#3#4#5#6#7#8#9#:#;#<#$$$ $ $$$$$$$"$%$($+$.$1$4$7$:$>%lightspeed ribbon= {superstring}lightspeed telegraph= {telegraph}.lightspeed wireAny {wick} that can {burn} non-destructively at the speed of light. Lightspeed wires are a type of {reburnable fuse}. These are potentially useful for various things, but so far the necessary mechanisms are very large and unwieldy. In October 2002, Jason Summers discovered a lightspeed reaction travelling through an orthogonal chain of beehives. Summers completed a period-1440 lightspeed {telegraph} based on this reaction in 2003. A {stable} lightspeed {transceiver} mechanism using this same signal reaction, the {p1 telegraph}, was constructed by Adam P. Goucher in 2010; the bounding boxes of both the {transmitter} and {receiver} are over 5000 cells on a side. A more compact periodic {high-bandwidth telegraph} with a much improved transmission rate was completed by Louis-Francois Handfield in 2017. The following diagram shows an older example of a lightspeed wire, with a small defect that travels along it at the speed of light. As of June 2018, no method has been found of creating such a defect in the upstream end of this particular stable wire, or of non-destructively detecting the arrival of the defect and repairing the wire at the downstream end.Z     #$()-.2378<=  "%'*,/1469;>   #$()-.2378<=  ?lightweight emulator= {LW emulator}lightweight spaceship= {LWSS}lightweight volcano = {toaster} linear growthA growth rate proportional to T, where T is the number of ticks that a pattern has been run. Compare {superlinear growth}, {quadratic growth}.linear propagatorA self-replicating pattern in which each copy of a pattern produces one child that is an exact copy of itself. The child pattern then blocks the parent from any further replication. An example was constructed by Dave Greene on 23 November 2013, with a construction arm using two glider lanes separated by {9hd}. By some definitions, due to its limited one-dimensional growth pattern, the linear propagator is not a true replicator. Compare {quadratic replicator}. line crosserA pattern which is able to send a signal across an infinite diagonal line of live cells without destroying the line. David Bell built one in August 2006. It uses many one-shot period 44160 {glider gun}s on both sides of the line having the proper synchronization to create the reactions shown in {line-cutting reaction} and {line-mending reaction}. An input glider can arrive at any multiple of 44160 generations to first cut the line, then send a glider through the gap, and finally mend the line while leaving an output glider on the other side. A line crosser whose complete mechanism is on one side of the line is theoretically possible, using {single-channel} construction methods for example.line-cutting reactionA reaction that can cut an infinite diagonal line of cells, leaving a gap with both ends sealed. Such a reaction is demonstrated below. In actual use the reaction should be spread out so that the incoming {LWSS}es don't conflict. See {line-mending reaction} for a way to mend the gap.            ! " #  $    % &'()*+,-#$.$%/#012%&'3$'4'5'6$&78 9!;!"" ":";" ##### #+#,#-#.#$$$ $*$.$%%.%*&-&4*5*5+6+4,8.9.:.8/;/808192;233445*7)8*8+8)9+9,9*:+:,:*;+;<<line-mending reaction A reaction which can fully mend a sealed gap in an infinite diagonal line of cells, such as the one produced by a {line-cutting reaction}. Such a reaction is demonstrated below. See the line cutting reaction for a way of creating the gliders travelling parallel to the line. This reaction uses spaceships on both sides of the line which need to be synchronized to each other, for example by passing a glider through the gap to trigger the creation of the required spaceships and gliders. No simple mechanism is known to mend the gap which lies completely on one side of the line. However, it is technically possible to use {construction arm} {technology} to push objects through the gap to build and trigger a {seed} for the required {synchronized} {signal}s on the other side.   42334   + -  + ,  , *))*++-+,47,3#$%37%3456$'(')* +!" ","# #-# $.$6$7$ %(%)%/%5%6% &&(&*&0&7& ''''('1'((2())3)***4*+++ +5+, ,6,7-9-8.9.!9 :!:":; ;";< <!< =!=:> line pufferGA {puffer} which produces its output by means of an orthogonal line of cells at right angles to the direction of travel. The archetypal line puffer was found by Alan Hensel in March 1994, based on a {spaceship} found earlier that month by Hartmut Holzwart. The following month Holzwart found a way to make {extensible} c/2 line puffers, and Hensel found a much smaller stabilization the following day. But in October 1995 Tim Coe discovered that for large widths these were often unstable, although typically lasting millions of generations. In May 1996, however, Coe found a way to fix the instability. The resulting puffers appear to be completely stable and to exhibit an exponential increase in period as a function of width, although neither of these things has been proved. Line puffers have enabled the construction of various difficult periods for c/2 spaceships and puffers, including occasionally periods which are not multiples of 4 and which would therefore be impossible to attain with the usual type of construction based on {standard spaceship}s. (See {frothing puffer} for another method of constructing such periods.) In particular, the first c/2 {rake} with period not divisible by 4 was achieved in January 2000 when David Bell constructed a p42 {backrake} by means of line puffers. See also {hivenudger} and {puff suppressor}. line ship`A {spaceship} in which the front end is a {linestretcher}, the line being eaten by the back end. linestretcher!A {wickstretcher} that stretches a single diagonal line of cells. The first example was constructed by Jason Summers in March 1999; this was c/12 and used {switch engine} based puffers found earlier by Dean Hickerson. The first c/4 example was found by Hartmut Holzwart in November 2004. loading dock)Found by Dave Buckingham, September 1972.p3 loafp1loaferPA small {c/7 spaceship} discovered by Josh Ball on 17 February 2013: It has a known 8-glider construction recipe, probably not minimal, discovered on the following day: The loafer was therefore the first new glider-constructible spaceship in almost a decade. (A {glider synthesis} for a 2c/5 ship, {60P5H2V0}, was found in March 2003.)c/7 orthogonallyp7 loaflipflopRHere four {pentadecathlon}s {hassle} a {loaf}. Found by Robert Wainwright in 1990.p15O               !!!   !!!"" loaf on loaf = {bi-loaf} loaf pullWThe following glider/loaf collision, which pulls a loaf (3,1) toward the glider source:  loaf siamese bargep1 lobsterA spaceship discovered by Matthias Merzenich in August 2011, the first diagonally travelling {c/7 spaceship} to be found. It consists of two {glider}s pulling a {tagalong} that then rephases them.c/7 diagonallyp7S                               logarithmic growthA pattern whose {population} or {bounding box} grows no faster than logarithmically, asymptotic to n.log(t) for some constant n. The first such pattern constructed was the {caber tosser} whose population is logarithmic, but whose bounding box still grows linearly. The first pattern whose bounding box and population both grow logarithmically was constructed by Jason Summers with Gabriel Nivasch in 2003. For a pattern with a slower growth rate than this, see {Osqrtlogt}.LoM= {lumps of muck} lone dot agar2An {agar} in which every live cell is isolated in every generation. There are many different lone dot agars. All of them are {phoenix}es. In 1995 Dean Hickerson and Alan W. Hensel found stabilizations for finite patches of ten lone dot agars to create period 2 oscillators. One of these is shown below:@  !  !   $%  "% $ !  #%        ! $ %               $ %       " %  $ !  #% !$%   $%  "% $ !  #% !$%   $%  "% $ !       # % !!! !!!!!!!!$!%!" """### #$$ $ $$$$$$$$!$%%% % % %%%%%%%%% %!%&& lonely bee= {worker bee}longA term applied to an object that is of the same basic form as some standard object, but longer. For examples see {long barge}, {long boat}, {long bookend}, {long canoe}, {long shillelagh}, {long ship} and {long snake}.long^3PThe next degree of longness after {long long}. Some people prefer "extra long".long^4SThe next degree of longness after {long^3}. Some people prefer "extra extra long". long bargep1 long boatJ A long boat can be used as a 90-degree or 180-degree {one-time} {turner}.p1 long bookend8The following {induction coil}, longer than a {bookend}. long canoep1 long hat= {loop} long hook= {long bookend} long house= {dock} long integralp1  long longJThe next degree of longness after {long}. Some people prefer "very long".long long bargep1 long long boatp1 long long canoep1 long long shipp1 long long snakep1long shillelaghp1  long shipp1long sinking ship= {long canoe} long snakep1loopp1 looping spaceship%= {reflectorless rotating oscillator}lossless elbowXA stationary {elbow} in a {construction arm} {toolkit} that allows a {recipe} to turn a corner with no exponential increase in construction cost. Compare {slow elbow}. It is theoretically possible to construct lossless elbows for early construction arms such as the one in the {10hd Demonoid}, but these would currently have to be very large. The lossless elbow that has been used the most in practice is the {Snark}, which can be constructed directly on a {single-channel} {construction lane} using a {Snarkmaker} {recipe}. Controlled demolition of a Snark is also possible, to remove a temporary elbow that is no longer needed, and leave a {hand} target in its place if necessary for further construction. A {Silver reflector} was used as a lossless elbow in the first {spiral growth} pattern, attached to a separate {universal constructor} component.low-density Life= {sparse Life} lumps of muckThe common evolutionary sequence that ends in the {blockade}. The name is sometimes used of the blockade itself, and can in general be used of any stage of the evolution of the {stairstep hexomino}. LW emulatorTThe smallest (and least useful) {emulator}, found by Robert Wainwright in June 1980.p4           LWSSA lightweight spaceship, the smallest known orthogonally moving {spaceship}, and the second most common (after the {glider}). Found by Conway when one formed from a random soup in 1970. See also {MWSS} and {HWSS}. The LWSS possesses a {tail spark} which can easily {perturb} other objects which grow into its path. The spaceship can also perturb some objects in additional ways. For examples, see {blinker ship}, {hivenudger}, and {puffer train}. Dave Buckingham found that the LWSS can be synthesized in several different ways using three gliders, and can be constructed from two gliders and another small object in several more ways. Here is the fastest {synthesis}:c/2 orthogonallyp4  LWSS emulator= {LW emulator}LWSS-glider bounceThe following reaction in which a {LWSS} and a {glider} collide to form a glider heading back between the two input paths: This is one way to {inject} a glider into a existing glider stream. The {infinite glider hotel} uses this reaction.      LWSS-LWSS bounce%The following {symmetric} reaction in which two {LWSS}s collide head-on to form two {glider}s heading apart at 90 degrees from each other. Compare {LWSS-LWSS deflection}. This provides one way to {inject} a {glider} into a existing glider stream. Another use is described in {metamorphosis}.       LWSS-LWSS deflectionThe following symmetric reaction in which two LWSSs collide nearly head-on to form two gliders heading apart at 180 degrees from each other. Compare {LWSS-LWSS bounce}.      LWSS-to-GSee {135-degree MWSS-to-G}.LWTDSLife Worker Time Deficiency Syndrome. Term coined by Dieter Leithner to describe the problem of having to divide scarce time between Life and real life. LW volcano = {toaster}Lx200 A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Paul Callahan in June 1997. It is made up of two {elementary conduit}s, HL141B + {BFx59H}. The Lx200 and {F166} conduits are the two original {dependent conduit}s (several more have since been discovered.) After 200 ticks, it produces an inverted {Herschel} turned 90 degrees counterclockwise at (17, -40) relative to the input. Its {recovery time} is 90 ticks. It can be made {Spartan} by replacing the {snake}s with {eater1}s in one of two orientations. A {ghost Herschel} in the pattern below marks the output location: The input shown here is a {Herschel great-grandparent}, since the input reaction is catalysed by the {transparent} block before the Herschel's standard form can appear.Q !! %!% &"&''"'((((("(#()))))) )****** *++ /!/ 0!0223444 4!45 5!5667789999:;;;<$= macrocell^A format used by {Golly} and its {hashlife} algorithm, capable of storing repetitive patterns very efficiently, even if they contain a large number of cells. For example, a filled square 2^167 cells on a side can be stored in less than three kilobytes in macrocell format, or about 800 bytes in compressed macrocell format. The square's total population is over a googol, 10^100; the number of atoms in the observable universe is only about 10^80. This high level of compression is obtained by defining a tree structure composed of increasingly large cell "tiles" with power-of-two dimensions. Tile definitions of any size are re-used whenever they appear multiple times in a large pattern (at the same power-of-two offset). For example, the following is a macrocell encoding of a complex {pseudo still life} arrangement of {ship}s, with a total population over 2500 cells: The first line after the #R rule line defines a quadtree tile at the lowest level - a level-3 tile in this case, meaning a 2^3 square area. At this level the pattern is encoded in a modified ASCII format with dollar signs as line separators. The next line, #2, defines a level-4 quadtree tile, made from one empty level-3 tile in the northwest corner (0), and three copies of the level-3 tile that was defined on the previous line (1). Lines 3, 4, and 5 similarly define level 5, 6, and 7 quadtree tiles by giving the line numbers of four tiles of the next lower size. Many patterns are only moderately repetitive, so macrocell format is somewhat less successful at compressing them. Certainly most patterns are not nearly as regular as the artificial example above: there are usually many different tiles defined at each level, not just one. Chaotic patterns, such as {ash} from random {soup}s, usually need so many different tile definitions that they can be stored more efficiently using {rle} format.    "$&)*,- macro-spaceship"A {self-constructing} or {self-supporting} {spaceship}, such as the {Caterpillar}, {Centipede}, {half-baked knightship}, {waterbear}, {Demonoid}, {Orthogonoid}, and {Caterloopillar}. Engineered spaceships of these types tend to be much larger and more complex than {elementary} spaceships.mango~A relatively rare 180-degree rotationally {symmetric} 8-{bit} {still life}. The {acorn} produces a mango as part of its {ash}.p1 mathematicianFound by Dave Buckingham, 1972.p5#       MaxA name for the smallest known {spacefiller}. The name represents the fact that the growth rate is the fastest possible. (This has not quite been proved, however. There remains the possibility, albeit not very likely, that a periodic {agar} could have an average {density} greater than 1/2, and a spacefiller stretching such an agar at the same speed as the known spacefillers would have a faster average growth rate.)mazingIn terms of its minimum {population} of 12 this ties with {mold} as the smallest p4 {oscillator}. Found by Dave Buckingham in December 1973. For some constructions using mazings, see {popover} and {sixty-nine}.p4 mc = {macrocell} medium fish= {MWSS}megacell= {p1 megacell}. memory cellA type of information storage {circuit} useful in many patterns that perform complex logical operations. Most commonly a memory cell can store a single bit of information. See for example {demultiplexer}, {honey bit}, and {boat-bit}. Depending on the application, the circuit may be a {toggle circuit} or a {permanent switch}, or it may be possible to send one or more signals to set the circuit to a "1" state, as can be done with a {keeper} mechanism. In that case a different input signal must be used to test the current state, usually with a {destructive read} reaction. A more complicated example can be found in the {Osqrtlogt} pattern, which destructively reads a growing 2-dimensional array of minimal memory cells. Each memory cell may either contain a {boat} (below left) or empty space (below right), with no permanent circuitry anywhere near: The two {beehive}s and the {block} are placed by {slow salvo}s, after an initial 90-degree {2-glider collision} that produces a target {honey farm}. The beehive {constellation} acts as a {one-time} {turner} for an incoming {glider}. If the boat is present, it acts as a second one-time turner for that glider, sending back a "1" signal. The "backstop" {block} in the northeast is destroyed cleanly in either the "0" or the "1" case./)*)*      !   "   !        #$% # $+Merzenich's p11-Found by Matthias Merzenich in December 2010.p11L                                      Merzenich's p18)Found by Matthias Merzenich in June 2011.p18G                            metacatacrystPA 52-cell pattern exhibiting quadratic growth. Found by Nick Gotts, December 2000. This was for some time the smallest known pattern (in terms of initial population) with superlinear growth. See {switch-engine ping-pong} for the lowest-population {superlinear growth} pattern as of July 2018, along with a list of the record-holders.metacellgCA logic circuitry that emulates the behavior of a single cell. The circuitry is hard-wired to emulate a particular CA rule, but changing the rule is usually a matter of making simple adjustments. Known examples include David Bell's original 500x500 {unit Life cell}, Jared Prince's {Deep Cell}, Brice Due's {OTCA metapixel}, and Adam P. Goucher's {megacell}. metamorphosisJAn {oscillator} built by Robert Wainwright that uses the following reaction (found by Bill Gosper) to turn {glider}s into {LWSS}, and converts these LWSS back into gliders by colliding them head on using an {LWSS-LWSS bounce}. There are two ways to do the following reaction, because the {twin bees shuttle spark} is {symmetric}.5                        metamorphosis II3An oscillator built by Robert Wainwright in December 1994 based on the following p30 {glider}-to-{LWSS} {converter} using a {queen bee shuttle pair}. This converter was first found by Paul Rendell, January 1986 or earlier, but wasn't widely known about until Paul Callahan rediscovered it in December 1994.8             metapixel!See {metacell}, {OTCA metapixel}. methuselahAny small pattern that stabilizes only after a long time. Term coined by Conway. Examples include {rabbits}, {acorn}, the {R-pentomino}, {blom}, {Iwona}, {Justyna} and {Lidka}. See also {ark}. Mickey Mouse2The following {still life}, named by Mark Niemiec:p1   middleweight emulator= {MW emulator}middleweight spaceship= {MWSS}middleweight volcano= {MW volcano}mini pressure cookerHFound by Robert Wainwright before June 1972. Compare {pressure cooker}.p3    M.I.P. valueThe maximum {population} divided by the initial population for an unstable pattern. For example, the {R-pentomino} has an M.I.P. value of 63.8, since its maximum population is 319. The term is no longer in use.MIT oscillator = {cuphook} MMM breederSee {breeder}. MMS breederSee {breeder}.modThe smallest number of generations it takes for an {oscillator} or {spaceship} to reappear in its original form, possibly subject to some rotation or reflection. The mod may be equal to the {period}, but it may also be a quarter of the period (for oscillators that rotate 90 degrees every quarter period) or half the period (for other oscillators which rotate 180 degrees every half period, and also for {flipper}s).moldFound by Achim Flammenkamp in 1988, but not widely known until Dean Hickerson rediscovered it (and named it) in August 1989. Compare with {jam}. In terms of its minimum {population} of 12 it ties with {mazing} as the smallest p4 {oscillator}. But in terms of its 6x6 {bounding box} it wins outright. In fact, of all oscillators that fit in a 6x7 box it is the only one with {period} greater than 2.p4 monochromatic salvoA {slow salvo} that uses gliders of only one colour. For example, the slow salvos generated by {half-baked knightship}s are monochromatic, because they are generated by a single type of reaction which can happen at any position along a diagonal line. The smallest possible step size is one {full diagonal} (1fd), which is two {half diagonal}s (2hd), which means that any single glider-producing reaction can only reach half of the available glider {lane}s. See {colour of a glider}.monogram%Found by Dean Hickerson, August 1989.p4monoparity salvoVA {slow salvo} that uses gliders of only one {parity}. Compare {monochromatic salvo}.Moore neighbourhoodThe set of all cells that are orthogonally or diagonally adjacent to a cell or group of cells. The Moore neighbourhood of a cell can be thought of as the points at a Chebyshev distance of 1 from that cell. Compare {von Neumann neighbourhood}. The Conway's Life rule is based on the Moore neighborhood, as are all the "Life-like" rules and many other commonly investigated rule families. Cell neighbourhoods can also be defined with a higher range. The Moore neighbourhood of range n can be defined recursively as the Moore neighbourhood of the Moore neighbourhood of range n-1. For example, the Moore neighbourhood of range 2 includes all cells that are orthogonally or diagonally adjacent to the standard Moore neighbourhood. moose antlersp1 mosquitoGSee {mosquito1}, {mosquito2}. {mosquito3}, {mosquito4} and {mosquito5}. mosquito1A {breeder} constructed by Nick Gotts in September 1998. The original version had an initial population of 103, which was then the smallest for any known pattern with superlinear growth (beating the record previously held by {Jaws}). This was reduced to 97 by Stephen Silver the following month, but was then almost immediately superseded by {mosquito2}. Mosquito1 consists of the classic {puffer train} plus four {LWSS} and four {MWSS} (mostly in {predecessor} form, to keep the population down). Once it gets going it produces a new block-laying {switch engine} (plus a lot of junk) every 280 generations. It is therefore an MMS breeder, albeit a messy one. mosquito2 A {breeder} constructed by Nick Gotts in October 1998. Its initial population of 85 was for a couple of hours the smallest for any known pattern with superlinear growth, but was then beaten by {mosquito3}. Mosquito2 is very like {mosquito1}, but uses two fewer {MWSS} and one more {LWSS}. mosquito3A {breeder} constructed by Nick Gotts in October 1998. Its initial population of 75 was at the time the smallest for any known pattern with superlinear growth, but was beaten a few days later by {mosquito4}. Mosquito3 has one less {LWSS} than {mosquito2}. It is somewhat different from the earlier mosquitoes in that the {switch engine}s it makes are glider-producing rather than block-laying. mosquito4A slightly improved version of {mosquito3} which Stephen Silver produced in October 1998 making use of another discovery of Nick Gotts (September 1997): an 8-cell pattern that evolves into a {LWSS} plus some junk. Mosquito4 is a {breeder} with an initial population of 73, at the time the smallest for any known pattern with superlinear growth, but superseded a few days later by {mosquito5}. mosquito5A slightly improved version of {mosquito4} which Nick Gotts produced in October 1998. The improvement is of a similar nature to the improvement of mosquito4 over mosquito3. Mosquito5 is a {breeder} with an initial population of 71. This was the smallest population for any known pattern with superlinear growth until it was superseded by {teeth}. See {switch-engine ping-pong} for the smallest such pattern as of July 2018, along with a list of the record-holders.mould= {mold}moving sawtoothA {sawtooth} such that no cell is ON for more than a finite number generations. David Bell constructed the first pattern of this type, with a c/2 front end and a c/3 back end. The front end is a {blinker puffer}. The back end ignites the {blinker fuse}. The smallest currently known moving sawtooth was constructed in April 2011 by a conwaylife.com forum user with the handle 'cloudy197'. The c/2 front end is a {bi-block puffer}. The 2c/5 back end ignites the {bi-block fuse}. MSM breederSee {breeder}.multiple roteightorsvAn {extensible} oscillator family consisting of one or more {roteightor} rotors, discovered by Dean Hickerson in 1990.p8                                          multiplicityIn a {reflectorless rotating oscillator}, the maximum number n of independent patterns that can orbit a single point, in a way that reduces the period of the combined oscillator by a factor of n.multi-state Life= {colourised Life}multum in parvoRA {methuselah} found by Charles Corderman, but not as long-lasting as his {acorn}.stabilizes at time 3933muttering moatAny {oscillator} whose {rotor} consists of a closed chain of cells each of which is adjacent to exactly two other rotor cells. Compare {babbling brook}. Examples include the {bipole}, the {blinker}, the {clock}, the {cuphook}, the {Gray counter}, the {quad}, the {scrubber}, the {skewed quad} and the p2 {snake pit}. The following diagram shows a p2 example (by Dean Hickerson, May 1993) with a larger rotor. See {ring of fire} for a very large one. MW emulatorKFound by Robert Wainwright in June 1980. See also {emulator} and {filter}.p4             MWSS-A middleweight spaceship, the third most common {spaceship}. Found by Conway in 1970 by modifying a {LWSS}. See also {HWSS}. The MWSS possesses both a {tail spark} and a {belly spark} which can easily perturb other objects as it passes by. The spaceship can also perturb some objects in additional ways. For examples see {blinker puffer} and {glider turner}. Dave Buckingham found that the MWSS can be synthesized using three gliders, and can be constructed from two gliders and another small object in several more ways. Here is the {glider synthesis}:c/2 orthogonallyp4  MWSS emulator= {MW emulator}MWSS out of the blueThe following reaction, found by Peter Rott in November 1997, in which a {LWSS} passing by a p46 {oscillator} creates a {MWSS} travelling in the opposite direction. Together with some reactions found by Dieter Leithner, and an LWSS-turning reaction which Rott had found in November 1993 (but which was not widely known until Paul Callahan rediscovered it in June 1994) this can be used to prove that there exist {gliderless} guns for LWSS, MWSS and {HWSS} for every period that is a multiple of 46.\  # $   # $                   #$  #$          '' ' '(( ( (%) MWSS-to-G2See {135-degree MWSS-to-G}, {45-degree MWSS-to-G}. MW volcano&Found by Dean Hickerson in April 1992.p54                        .My Experience with B-heptominos in OscillatorsAn article by Dave Buckingham (October 1996) available from {http://conwaylife.com/ref/lifepage/patterns/bhept/bhept.html}. It describes his discovery of {Herschel conduit}s, including sufficient (indeed ample) {stable} conduits to enable, for the first time, the construction of period n oscillators and {true} period n guns for every sufficiently large integer n. See {Herschel loop} and {emu}.naturalAOccurring often in random patterns. There is no precise measure of naturalness, since the most useful definition of "random" in this context is open to debate. Nonetheless, it is clear that objects such as {block}s, {blinker}s, {beehive}s and {glider}s are very natural, while {eater2}s, {dart}s, {gun}s, etc., are not.natural Heisenburp A {twin bees shuttle pair} arrangement found by Brice Due in 2006. A {glider} passes through the reaction area of the shuttle pair completely unaffected. However, a {Heisenburp effect} causes a second glider to be created "out of the blue", following behind the first at a 2{hd} offset.p46C#$#$ #$   # $   %%%%&&&&%'ND read= {non-destructive read}negative spaceshipA type of {signal} travelling through a periodic {agar} such as {zebra stripes}. The leading edge of the signal removes the agar, and the trailing edge rebuilds the agar some time later. The distance between the two edges is sometimes adjustable, as shown in {lightspeed bubble}. The central part of the "spaceship" may consist of dying sparks or even simple empty space. Below is a sample period-5 negative spaceship, found by Hartmut Holzwart in March 2007, in a small stabilized section of {zebra stripes} agar: The "spaceship" travels to the left at the {speed of light}, so it will eventually reach the edge of any finite patch and destroy itself and its supporting agar. "%(+.147      !"#$%&'()*+,-./01234567      !"%&'()*+,-./01234567 $%8     !"&'(),-./01234567+,     !"()-.1234567 $&'018                      ! " & ' - . 2 3 4 5 6 7   ( ) + ,                        + , 2 3 4 5 6 7  - . 0 1 8                     ( 0 1 4 5 6 7 #'23      !"#$+34567 !%,8      !"#$+34567#'23     (014567-.018      +,234567()+,      !"&'-.234567 $&'018     !"()-.1234567+,     !"&'(),-./01234567 $%8      !"%&'()*+,-./01234567      !"#$%&'()*+,-./01234567         " % ( + . 1 4 7 9! negentropyCompare {Hertz oscillator}.p2$          neighbourAny of the eight cells adjacent to a given cell. A cell is therefore not considered to be a neighbour of itself, although the neighbourhood used in Life does in fact include this cell (see {cellular automaton}).new five&Found by Dean Hickerson, January 1990.p3 new gunpAn old name for the period 46 glider gun show below. This was found by Bill Gosper in 1971, and was the second basic glider gun found (after the {Gosper glider gun}). It produces a period 46 glider {stream}. A number of other ways of constructing a gun from two {twin bees shuttle}s have since been found. See {edge shooter} for one of these, and see also {p46 gun}.p468 ! !     !! !        !"" Noah's ark"The following diagonal {puffer} consisting of two {switch engine}s. This was found by Charles Corderman in 1971. The name comes from the variety of objects it leaves behind: blocks, blinkers, beehives, loaves, gliders, ships, boats, long boats, beacons and block on tables. See also {ark}.          n-omino%Any {polyomino} with exactly n cells.non-destructive readWA type of test reaction in {memory cell} circuitry, where the information in the memory cell is unchanged and can be read again to produce the same result. One simple type of non-destructive read reaction is a {signal} sent to a {permanent switch}. Memory cells with {destructive read} reactions are generally simpler and more commonly used. nonfiller= {space nonfiller} non-monotonicA {spaceship} is said to be non-monotonic if its leading edge falls back in some generations. The first example (shown below) was found by Hartmut Holzwart in August 1992. This is p4 and travels at c/4. In April 1994, Holzwart found examples of p3 spaceships with this property, and this is clearly the smallest possible period. Another non-monotonic spaceship is the {weekender}.B              "nonomino switch engine predecessorbThis is the unique nonomino (a {polyomino} having 9 cells) whose {evolution} results in a {switch engine}, and the smallest polyomino to do so. Charles Corderman may have found this object in 1971 while exhaustively investigating the {fate} of all the small {polyomino}es. Records indicate that he found the {switch engine} while investigating the decominoes (polyominoes having 10 cells). However, there do not appear to be decominoes which result in a {clean} {switch engine}. If Corderman was examining polyominoes in order of size, then this smaller {predecessor} should have been found first in any case.  non-sparkSomething that looks like a spark, but isn't. An {OWSS} produces one of these instead of a {belly spark}, and is destroyed by it.non-standard spaceship@Any {spaceship} other than a {glider}, {LWSS}, {MWSS} or {HWSS}. non-trivialA non-trivial period-N {oscillator} contains at least one cell that oscillates at the full period. In other words, it is not made up solely of separate oscillators with smaller periods. Usually it includes a {spark} or other reaction that would not occur if all lower-period subpatterns were separated from each other, but some exceptions are given under {trivial}. See also {omniperiodic}.novelty generatorA pattern that appears to have an {unknown fate} due to complex feedback loops, for example involving {wave}s of gliders shuttling between perpendicular {rake}s. Novelty generator patterns fall short of counting as {chaotic growth}, since the rakes continue to be predictable, and much of their {ash} generally remains stable. It has not been proven conclusively that any particular pattern is in fact an infinite novelty generator, since it is always possible that periodicity will spontaneously arise if the simulation is continued far enough. In fact this happens quite regularly. But conversely, it has not been proven that periodicity must spontaneously arise for all such patterns. Bill Gosper, Nick Gotts and others have done extensive experiments along these lines using {Golly}.NW31One of the most common stable {edge shooter}s. This {Herschel-to-glider} {converter} suppresses the junk ordinarily left behind by an evolving {Herschel} while allowing both the {first natural glider} and {second natural glider} to escape on {transparent lane}s: The edge shooter output at the top has no additional {clearance}, so its use in creating {convoy}s is limited: it can only add gliders on the outermost lanes of an existing glider {salvo}. Like the beehive version of {SW-2}, either output can be used to build logical OR gates, where multiple input {signal} paths are merged onto the same output path. The complete name for this converter is "NW31T120", where 31 is the output glider lane number. In the above orientation, lane numbers get bigger toward the upper right and smaller toward the lower left (and may easily be negative). The T120 timing measurement means that a canonical NW glider placed on lane 31 at time T=120, at (+31, +0) relative to the input Herschel, would in theory reach the exact same spacetime locations as the converter's output glider does. Most converters are not edge shooters and their output lanes are not transparent, so they usually have catalysts that would interfere with this theoretically equivalent glider. This is the case for the optional third glider output created by the lower {eater1} catalyst: the upper eater1 overlaps its {lane}. For the alternate {block} catalyst suppressing this glider output, see {transparent lane}.             NW31T120= {NW31}oblique8Neither diagonal nor orthogonal. See also {knightship}. obo spark?A {spark} of the form O.O (so called after its {rle} encoding). octagon IIThe first known p5 {oscillator}, discovered in 1971 independently by Sol Goodman and Arthur Taber. The name is due to the latter.p5 octagon IV)Found by Robert Wainwright, January 1979.p4(            octominoAny 8-cell {polyomino}. There are 369 such objects. The word is particularly applied to the following octomino (or its two-generation successor), which is fairly common but lacks a proper name:odd keysMFound by Dean Hickerson, August 1989. See also {short keys} and {bent keys}.p3     omino = {polyomino} omniperiodicA {cellular automaton} is said to be omniperiodic if it has {oscillator}s of all {period}s. It is not known if Life is omniperiodic, although this seems likely. Dave Buckingham's work on Herschel conduits in 1996 (see {My Experience with B-heptominos in Oscillators}) left only a short list of unresolved cases, all with periods of 58 or below. The list has been progressively reduced since then. Most recently, period 43 and 53 oscillators were made possible in 2013 by Mike Playle's {Snark}. As of June 2018, no oscillators are known for periods 19, 23, 38, or 41. If we insist that the oscillator must be {non-trivial}, then 34 should be added to this list. Note that if we were to allow infinite oscillators, then all periods are certainly possible, as any period of 14 or more can be obtained using a {glider} (or {LWSS}) stream, or an infinitely long {2c/3} wire containing signals with the desired separation.one per generationSee {grow-by-one object}.one-sided spaceship synthesisA {glider synthesis} of a {spaceship} in which all gliders come from the same side of the spaceship's path. Such syntheses are used extensively in the 17c/45 {Caterpillar}. For example, here is a one-sided way to create an {LWSS}.     one-timeBA term used for {turner}s and {splitter}s, specifying that the reaction in question is not repeatable as it would be in a {reflector} or {fanout} device. Instead, the {constellation} is used up, usually in a {clean} reaction, but the much more common {dirty} turners and splitters are also very useful in some situations. onion ringsFor each integer n>1 onion rings of order n is a {stable} {agar} of {density} 1/2 obtained by tiling the plane with a certain 4n x 4n pattern. The tile for order 3 onion rings is shown below. The reader should be able to deduce the form of tiles of other orders.H                          Online Life-Like CA Soup Search(= {The Online Life-Like CA Soup Search}.on-offAny p2 {oscillator} in which all {rotor} cells die from {overpopulation}. The simplest example is a {beacon}. Compare {flip-flop}. O-pentominowConway's name for the following {pentomino}, a {traffic light} {predecessor}, although not one of the more common ones.orbitA term proposed by Jason Summers to refer to a natural stabilization of a {puffer}. For example, the {switch engine} has two (known) orbits, the block-laying one and the glider-producing one.OrionfFound by Hartmut Holzwart, April 1993. In May 1999, Jason Summers found the following smaller variant:c/4 diagonallyp4'                  orphanConway's preferred term for a {Garden of Eden}. According to some definitions, an orphan consists of just the minimum living and dead cells needed to ensure that no parent is possible, whereas a GoE is an entire infinite Life plane that contains an orphan. Orthogonoid-A {self-constructing} {spaceship} analogous to the {Demonoid}s, with a slow orthogonal direction of travel. The first example was completed by Dave Greene on 29 June 2017, with a top speed of 16c/217251 (this is just 256c/3476016 in lowest terms). The construction recipe is a stream of MWSSes, with the recovery time limited to 90 ticks by the {Lx200} {dependent conduit} that follows the initial {syringe} converter. The design is {hashlife}-friendly, meaning that the spaceship can be trivially adjusted so that spatial and temporal offsets are exact powers of two; period 4194304 and period 8388608 versions have been constructed, with speeds of c/16384 and c/32768 respectively. The MWSSes are converted to {Herschel}s, which produce a standard {single-channel} glider stream that runs the Orthogonoid's single construction arm. After the child circuitry is complete, a previously constructed {Snark} in the parent is removed from the construction arm lane, converting it to a "destruction arm" that shoots down the previous constructor/reflector in the series. 256c/3476016p3476016 oscillator Any pattern that is a {predecessor} of itself. The term is usually restricted to non-{stable} finite patterns; period 1 oscillators are {stable} and are usually just called {still life}s. The {blinker} is the smallest non-stable oscillator, having period 2. There are oscillators of almost all higher periods (see {omniperiodic}). In general {cellular automaton} theory the term "oscillator" usually covers {spaceship}s as well, but this usage is not normal in Life. Oscillators consisting of separate objects which do not react in any phase are usually ignored. For example, a separated {blinker} and {pulsar} makes a period 6 oscillator, but is considered {trivial}. An oscillator can be divided into a {rotor} and a {stator}, and the stator can be further subdivided into {bushing} and {casing}. Some oscillators have no casing cells, and a few 100%-{volatility} oscillators also have no bushing cells. An oscillator can be constructed from any {gun} as long as {eater}s can be added to consume its output. If it is a {true} {gun} then the period of the oscillator will be the same as the gun - unless the eating mechanism multiplies the period, as in the case of gliders caught by a {boat-bit}. With the discovery of {reflector}s, {relay}s provide an easy way to create oscillators of all large periods. For example, eight gliders travelling in a loop created by four {Snark}s can create any period above 42, with a population never exceeding 356 live cells. For the very lowest periods, whole families of {extensible} oscillators are known. Examples of this are {barberpole}, {cross}, {pentoad}, {p6 shuttle}, {snacker}, and {multiple roteightors}. Any of the {shuttle}s are oscillators by definition, for example the {queen bee shuttle}. Many of these are also extensible. Other oscillators such as {figure-8} and {tumbler} have unique mechanisms that are not part of an extended family. Some oscillators are useful because of the {perturbation}s they can cause to other objects. This is especially true if they provide a {spark} on their boundary. Some oscillators are explicitly found by {search program}s in order to produce these sparks, such as {pipsquirter}s. Some higher period oscillators have been found while running random {soup}s. This is especially true if the soup is run on a cylindrical or torus {universe}. Sometimes the found objects can be moved to the normal universe and supported there by added {catalyst}s. {Achim's p144} is an example. Osqrtlogt8A pattern constructed by Adam P. Goucher in 2010, which uses an unbounded triangular region as memory for a binary counter. Empty space is read as a zero, and a boat as a one, as shown in the example pattern in {memory cell}. The pattern's diametric growth rate is O(sqrt(log(t))), which is the slowest possible for any Life pattern, or indeed any 2D Euclidean cellular automaton. The population returns infinitely often to its initial minimum value (during carry operations from 11111...1 to 100000...0, so it can be considered to be an unusual form of {sawtooth}. p1 circuitryOTCA metapixelA 2048 x 2048 period 35328 {metacell} constructed by Brice Due in 2006. It contains a large "pixel" area that contains a large population of {LWSS}es when the metacell state is ON, but is empty when it is OFF. This allows the state of the metacell to be visible at high zoom levels, unlike previous {unit cell}s where the state was signaled by the presence or absence of a single glider in a specific location. p46 circuitryout of the blueSee {natural Heisenburp}. Other similar mechanisms, particularly the method of {LWSS} creation used in the pixel part of the {OTCA metapixel}, may also be referred to as "out of the blue" reactions. overclockingvA term used when a {circuit} can accept a signal at a specific period which it cannot accept at a higher period. A {syringe} is a simple example. Some {staged recovery} circuits also permit overclocking, and can function successfully at a rate faster than their {recovery time}. A {Silver reflector} has a recovery time of 497 ticks, but can be overclocked to reflect a period 250 glider stream, or any nearby period above 248, simply by removing a beehive after the first glider enters the reflector. However, a continuous stream of gliders is then required to maintain the circuit, with timing within a tightly bounded range. overcrowding= {overpopulation} over-exposure= {underpopulation}overpopulation^Death of a cell caused by it having more than three {neighbour}s. See also {underpopulation}.over-unity reactionAn important concept in {gun} and {macro-spaceship} construction. To be a good candidate for building one of these types of patterns with a new period or speed, a stationary reaction (for a gun) or a moving reaction (for a macro-spaceship) must be able to produce some number of output {signal}s, strictly greater than the number of input signals required to maintain the reaction. The extra signal becomes a gun's output {stream}, or may be used in a variety of ways to construct the supporting {track} for a macro-spaceship. By implication, "over-unity" refers to the ratio of output signals to input signals. If all signal outputs must be used up to sustain a stationary reaction, a high-period {oscillator} may still be possible. See {emu} for example.overweight spaceship= {OWSS}OWSSA would-be {spaceship} similar to {LWSS}, {MWSS} and {HWSS} but longer. On its own an OWSS is unstable, but it can be escorted by true spaceships to form a {flotilla}.Ox2A 1976 novel by Piers Anthony which involves Life.p = {period}p13Period 1, i.e., {stable}. In the context of logic {circuit}ry, this tends to mean that a mechanism is constructed from {Herschel conduit}s that contain only {still life}s as {catalyst}s. In the context of {slow glider construction}, a P1 {slow salvo} is one in which there are no constraints on the {parity} of gliders in the salvo, because the {intermediate target}s are all stable constellations. (The usual alternative is a "P2 slow salvo", where the relative timing between adjacent gliders can be increased arbitrarily, but only by multiples of two ticks.)p104 gun{A {glider gun} with period 104, found by Noam Elkies on 21 March 1996. It is based on an {R-pentomino} {shuttle} reaction._   "# "#$  "#%  $&#&$%      $ %  $ %   $ %  $#%#%&$%$%' p11 bumpertA periodic {colour-preserving} {glider} {reflector} with a minimum {repeat time} of 44 ticks. Unlike the p5 through p8 cases where Noam Elkies' {domino}-spark based reflectors are available, no small period-22 {colour-changing} reflector is known. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams. In practice this reflector is not useful with input streams below period 121, because lower-period bumpers can be used to reflect all smaller multiples of 11 for which the bumper reaction can be made to work.p11b                                 p130 shuttleXA {shuttle} found in March 2004 by David Eppstein, which originally needed several period 5 oscillators for support. David Bell found a reaction between two of the shuttles to produce a p130 glider gun. On 18 November 2017 Tanner Jacobi found that the {stable} {sidesnagger} can be used to support the shuttle instead, and this is shown here.'('(&',-%(,-&('       *       ) +       * + *+)+*'&(%(,-&',-'('(.p144 gunA {glider gun} with {true} period 144. The first one was found by Bill Gosper in July 1994. For a full description and pattern see {factory}.p14 gunfA glider gun which emits a period 14 glider stream. This is the smallest possible period for any stream, so such a gun is of great interest. There is no known true-period p14 glider gun, and finding a small direct example is well beyond current search algorithms' abilities. However, pseudo-period p14 guns have been created by {inject}ing gliders into a higher period glider stream. The first pseudo p14 gun was built by Dieter Leithner in 1995. Smaller pseudo p14 guns have since been constructed, but they are still much too large to show here. The essential mechanism used by them is demonstrated in {GIG}. p15 bouncerNoam Elkies' {colour-changing} glider reflector, with {Karel's p15} providing the necessary {domino} {spark}. Compare to the {colour-preserving} {Snark}. The minimum {repeat time} is 30 ticks.@                             p15 bumperA periodic {colour-preserving} {glider} {reflector} with {Karel's p15} providing the necessary {spark}. The minimum {repeat time} is 45 ticks. For an equivalent {colour-changing} periodic glider reflector see {p15 bouncer}. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.:         p15 reflectoruAn ambiguous term that may refer to {PD-pair reflector}, {p15 bouncer}, or the more recently discovered {p15 bumper}.p184 gunA {true} period 184 {double-barrelled} glider gun found by Dave Buckingham in July 1996. The {engine} in this gun is a {Herschel descendant}. Unlike previous glider guns, the reaction flips on a diagonal so that both gliders travel in the same direction.&     p1 megacellA {metacell} constructed by Adam P. Goucher in 2008, capable of being programmed to emulate any Moore neighborhood rule, including isotropic and anisotropic non-totalistic rules. It fits in a 32768 by 32768 bounding box, with the resulting metacell grid at 45 degrees to the underlying Life grid. Like the {OTCA metapixel}, it includes a large "pixel" area so that the state of the megacell can easily be seen even at extremely small-scale zoom levels. p1 circuitry p1 telegraph{A variant of Jason Summers' {telegraph} pattern, constructed in 2010 by Adam P. Goucher using only stable circuitry. A single incoming glider produces the entire ten-part composite lightspeed signal that restores the beehive-chain {lightspeed wire} to its original position. The signal is detected at the other end of the telegraph and converted back into a single output signal. This simplification came at the cost of a much slower transmission speed, one bit per 91080 ticks. In this mechanism, sending the entire ten-part signal constitutes a '1' bit, and not sending the signal means '0'. See also {high-bandwidth telegraph}. p1 circuitryp22 gunA {true} period 22 {glider gun} constructed by David Eppstein in August 2000, using two interacting copies of a p22 oscillator found earlier the same day by Jason Summers.L$%"#&"#%&$%&)*)+#++ ,            -p246 gunA {true} period {glider gun} with period 246, discovered by Dave Buckingham in June 1996. The 180-degree mod-123 symmetry of its {bookend}-based {engine} makes it trivial to modify it into a {double-barrelled} gun. Its single-barreled form is shown below.W""#$ !%!#$&!$&$&'"$ "$!"$%          ) * )')'(     !!"##$$%%+&p24 gunuA {glider gun} with {true} period 24. The first one was found by Noam Elkies in June 1997. It uses three p4 {oscillator}s to {hassle} a pair of {traffic light}s. One of the oscillators was very large and custom-made. Shown below is a much smaller version built by Jason Summers and Karel Suhajda in December 2002, using the same mechanism but with a smaller oscillator::             %&( $&')       $ )   ! " $ & ' ) *       ! # % ' )      # % ' )      " $ & ' ) * "&( (  "$&'   !"  !  !$ !  !"  "$&'  ( "&(  "$&')*  #%')   !#%')  !"$&')* $)$&')%&(+ p256 gunPA {true} period 256 four-barrelled {glider gun} found by Dave Buckingham in September 1995. It uses four {R64} {conduit}s to make the second smallest known {Herschel loop} (after the {Simkin glider gun}). The p256 gun was an early "teaser" from Dave Buckingham before he released his full {Herschel} {technology}. Either {eater}s or {snake}s can be added as shown above, to suppress three of the glider streams so that only one stream escapes. This gun's p256 glider stream is well-suited for repeated reactions with receding {Cordership}s, or for "Hashlife-friendly" {signal} {circuit}ry.`  &'&'$%$%*+*+           +,+)+)*/0 / 0 !""##$$*$+$%*%+%.&/&.'/'(()) * *(*)* + +(+)+ . . / ///0011p29 pentadecathlon hasslerA {hassler} where two copies of a period 29 oscillator (which is itself a {pre-pulsar} hassler) change the period of a {pentadecathlon}. '/  &(.0 '/   56  ( . 6      ' ( ) - . / 6 8 9      ' ( ) - . / 5 6 9      # $ 2 7 8        " $ 2 3 4 5 6  "016!"()145()13  ,/13    ,-./12 0  .0  ./:p30 gunA {glider gun} with {true} period 30. The first one, found by Bill Gosper in November 1970 (see {Gosper glider gun}), was also the first gun found of any period. All known p30 glider guns are made from two or more interacting {queen bee shuttle}s. Paul Callahan found 30 different ways that three {queen bee shuttle}s can react to form a period 30 glider gun. One of the most interesting of these is shown below in which the gliders emerge in an unexpected direction.I                !" !## # $           % p30 reflector = {buckaroo} p30 shuttle= {queen bee shuttle}p36 gunA glider gun with {true} period 36. The first one was found by Jason Summers in 2004. Shown below is a smaller version using improvements by Adam P. Goucher and Scot Ellison:0./0--.! " # " $ ! $ % & #$*+#)+,),*+,&'*+%&'%(%&(.&'-.+,-0-/1.1/0      !!"" #### $$$ % %%% &&& ' ' ( ( ) ))$)%)**%*++++++ +!+"+#+$+,,,,,,,, ,!,",%,&,',------- -!-$-'-.%.&.////000021 p3 bumperA variant of Tanner Jacobi's {bumper} found by Arie Paap in April 2018. Two forms of the period 3 {oscillator} {catalyst} are shown below. For bounding box optimization purposes, it's also possible to replace the {eater1} in a p3, p6 or p9 bumper with another period 3 oscillator, saving one row along the south edge at the cost of a higher population. The {repeat time} for all these variants is 36 ticks, as shown.n !+,    " ' ) * + ,        ! % & ' * ,       % & '      $ & ' ( * , -   #(*+-#$'()&*+,'(),).p44 gun7A {glider gun} with a {true} period of 44. The first one was found by Dave Buckingham in April 1992. It uses two interacting copies of an {oscillator} which he also found. In 1996 he found a gun which only used one copy of the oscillator. Paul Callahan improved it in 1997, resulting in the gun shown below:s)*  ) +    & ' ) +    & ( *  (     & ) )%)%))&)(&(*&')+)+)*  "#"$  $ $!%!%%&&'((,) p44 MWSS gunjA gun discovered by Dieter Leithner in April 1997, in a somewhat larger form. This was the smallest known gliderless gun and smallest known MWSS gun until the construction in 2017 of the gun shown under {gliderless}, based on {Tanner's p46}. The p44 MWSS gun is based on a p44 oscillator discovered by Dave Buckingham in early 1992, shown here in an improved form found in January 2005 by Jason Summers using a new p4 {sparker} by Nicolay Beluchenko. A glider shape appears in this gun for three consecutive generations, but always as part of a larger {cluster}, so even a purist would regard this gun as gliderless.      ! !'()'*  '  ' +   '   ( *    ! !01 ,-/1 ,-/ 0!",-/0-/-/. !      !"### ####$$ $$$$$$$$%%% % % %%%%%%%%&&& &&'2(p45 gunA {true}-period glider gun discovered by Matthias Merzenich in April 2010. By most measures this is the smallest known odd-period gun of any type, either true-period or {pseudo}-period:          ! " & ) - . !"#$%*+,-.!"&)-.   "$#$   #    / -!/!."/"###$$$$$$$&&&&&&&'''0(p46 gunuA glider gun which has true-period 46. The first one found was the {new gun} by Bill Gosper in 1971. Prior to the discovery of {Tanner's p46} in October 2017, all known p46 guns were made from two or more {twin bees shuttle}s that interact (e.g., see {twin bees shuttle pair}). See {edge shooter} and {double-barrelled} for two more of these. On 21 October 2017 Heinrich Koenig found a glider gun using two copies of {Tanner's p46} placed at right angles to each other. This is the first p46 gun found which makes no use of the {twin bees shuttle}. See {gliderless} for a {MWSS} gun also made using two copies of Tanner's p46.\                  !  ! !"   !!!""""#####$%%#& p46 shuttle= {twin bees shuttle}p48 gunA {true} period compound {glider gun} based on the {p24 gun}, using a {Rich's p16} {oscillator} as a {filter} to remove half of the gliders from the {stream}.  !"!"!"                                         &'  %( $%  #$%+#&*, $%&*+  $%&*+  #&*, #$%+$%  %(  &'          ! !!!!!!!!!!!" " " """""# # ########$$ $$$$$$$$% % % %%%%%%%&&&&&&*&' ' ' ' ' '''''''+' ( ((()(*(+(-) p4 bumperA periodic {colour-preserving} {glider} {reflector} with a minimum {repeat time} of 36. Unlike the p5 through p8 cases where Noam Elkies' {domino} spark-based reflectors are available, no small period-4 {colour-changing} reflector is known. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.p4.           p4 reflector The following {glider} {reflector}, discovered by Karel Suhajda in October 2012. Its minimum repeat time is 52 ticks. Unlike the various {bouncer}s discovered many years earlier, it is a {colour-preserving} reflector, so it was made obsolete the following year by the discovery of the much smaller stable {Snark}, which uses the same initial {bait} reaction and so produces an output glider with the same timing. For a smaller periodic {colour-preserving} glider reflector with a different output timing, see {p4 bumper}.a  !)+(*+&'(.%)*+,-./0"$&)1"#$%'(*+,-./02#$%+-0256 % & ' ) + / 0 2 4 6    ! $ % ' ( ) * + 0 2 4   # $ % ' ( * - / 0 1 2 5 8 9   " ' * - 1 6 9     # * - 2 3 4 5 6 7 8  #&)3"%156 !"#$-.02346').02 !"#$%&')*+.0 (,.0"#$%(+-/"&(*-#$%')+,/ %)-./ !"%(*+ !"#$(*,-  '(,.#&'*,.!"#%&'*,./ #'*, "$%)*+,!"#%&')        " # !!!! !'!(!*!""""""&")"*"#&#'#:$ p54 shuttlegA surprising variant of the {twin bees shuttle} found by Dave Buckingham in 1973. See also {centinal}.p54D                           p5 bouncerA {colour-changing} glider reflector constructed by Noam Elkies in September 1998 by welding together two special-purpose period-5 {sparker}s. The minimum {repeat time} is 25 ticks. For {colour-preserving} glider reflectors see {p5 bumper} and the {stable} {Snark} reflector.p5                                                    p5 bumperA periodic {colour-preserving} {glider} {reflector} with a {middleweight volcano} producing the necessary {spark}. The minimum {repeat time} is 35 ticks. For an equivalent {colour-changing} periodic glider reflector see {p5 bouncer}. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.P                                   p5 reflectorTraditional name for {p5 bouncer} before 2016, but with the discovery of the {p5 bumper} this has become an ambiguous reference.p60 gunA glider gun with a {true} period of 60. The first one was found by Bill Gosper in 1970 and is shown below. There are several other ways to create a p60 gun from two p30 guns using period-doubling reactions similar to the one shown here.W      %& %&                !"!###$'p690 gun5A {true} period 690 {glider} gun found by Noam Elkies in July 1996. It is composed of a p30 {queen bee shuttle pair} and a p46 {twin bees shuttle} whose sparks occasionally react with each other. This is a very compact gun for such a high period and is used in many patterns requiring sparse glider streams.x          *+-%&'*+.&'.23'()-./03 (,012 (,012'()-./03!"&'.23 %&'*+. *+-4 p6 bouncer)Noam Elkies' {colour-changing} glider reflector using the {p6 pipsquirter}, with a minimum {repeat time} of 24 ticks. For {colour-preserving} glider reflectors see {p6 bumper} and the {stable} {Snark} reflector. with a {unix} providing the necessary {spark}. The minimum {repeat time} is 36 ticks. For an equivalent {colour-changing} periodic glider reflector see {p6 bouncer}. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.p6L                            p6 pipsquirterA {pipsquirter} oscillator found by Noam Elkies in November 1997, used in various {hassler}s and the colour-changing {p6 bouncer}.p65                      p6 reflectorTraditional name for {p6 bouncer} before 2016, but with the discovery of the {p6 bumper} this has become an ambiguous reference. p6 shuttleqThe following oscillator found by Nicolay Beluchenko in February 2004. This is {extensible} in more than one way:p6   p72 quasi-shuttleThe following {oscillator}, found by Jason Summers in August 2005. Although this looks at first sight like a {shuttle}, it isn't really.p72h ! ""#$  !# !"    !         !  !"  !#"#$ "! % p7 bouncerNoam Elkies' {colour-changing} {glider} {reflector} using a {p7 pipsquirter}, with a minimum {repeat time} of 28 ticks. A high-{clearance} version is shown in {p7 pipsquirter}. For {colour-preserving} glider reflectors see {p7 bumper} and the {stable} {Snark} reflector.p7p                                    p7 bumper[A periodic {colour-preserving} {glider} {reflector} with a minimum {repeat time} of 35 ticks. For an equivalent {colour-changing} periodic glider reflector see {p7 bouncer}. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.p79                     p7 pipsquirterA {pipsquirter} oscillator found by Noam Elkies in August 1999, used in various {hassler}s and the colour-changing {p7 reflector}. A larger period-7 pipsquirter is used in cases where space is limited where the reflector should extend southward for as short a distance as possible:V                          p7 reflectorTraditional name for {p7 bouncer} before 2016, but with the discovery of the {p7 bumper} this has become an ambiguous reference. p8 bouncerA glider {reflector} constructed by Noam Elkies in September 1998, with a minimum {repeat time} of 24 ticks. It is a {constellation} containing a {figure-8}, {boat}, {eater1}, and {block}. For {colour-preserving} glider reflectors see {p8 bumper} and the {stable} {Snark} reflector.(               p8 bumperA periodic {colour-preserving} {glider} {reflector} with a {blocker} attached to provide the necessary spark. The minimum {repeat time} is 40 ticks. For an equivalent {colour-changing} periodic glider reflector see {p8 bouncer}. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.(        p8 G-to-HcA small periodic variant of a stable two-glider-to-Herschel component found by Paul Callahan in November 1998 and used in the {Callahan G-to-H}, {Silver reflector} and {Silver G-to-H}. The minimum {repeat time} is 192 ticks, though some lower periods such as 96 are possible via {overclocking}. Here a {ghost Herschel} marks the output signal location:O          !   !               !"" p8 reflectorTraditional name for {p8 bouncer} before 2016, but with the discovery of the {p8 bumper} this has become an ambiguous reference.p90 gunA glider gun with {true} period 90. The one below by Dean Hickerson uses the output of two p30 guns in a period-multiplying reaction:h&&'() !'()*2"'*13 !'()*/04  &'()/04>?  &/04>? 13  2      ' )   ' (   ( +,+,()()*++@p92 gunA glider gun with a {true} period of 92. The first one was found by Bill Gosper in 1971 using a period doubling reaction using two p46 guns. Many different p92 guns are known that use multiple {twin bees shuttle}s. A period 92 gun can also be made by adding a {semi-cenark} to any period 46 glider gun. On 18 November 2017, Martin Grant found a new gun using one twin bees shuttle and one {Tanner's p46} oscillator, making it the smallest known p92 gun.  +,  +,   ,-  ,-                                 ,-   ,-+,+,    . p9 bumperA periodic {colour-preserving} {glider} {reflector} with a {repeat time} of 36. Unlike the p5 through p8 cases where Noam Elkies' {domino} spark-based reflectors are available, no small period-9 {colour-changing} reflector is known. A {stable} {Snark} reflector can be substituted for any {bumper}. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.?                   pair of bookends = {bookends}pair of tables= {table on table} paperclipA relatively 180-degree rotationally {symmetric} 14-{bit} {still life}. The {Iwona} {methuselah} contains a paperclip in its {ash}.p1parallel grey ship= {with-the-grain grey ship} Parallel HBKlc/245912, p245912) A much smaller successor to the {half-baked knightship}, constructed by Chris Cain in September 2014. Several slow-salvo recipes are needed to support the multi-glider salvo {seed}s at the upstream end of the spaceship. "Parallel" means that these recipes are sent in parallel instead of one after the other, in series, as in the original HBK.(6,3Parallel HBK gunAn {armless} constructor pattern that is programmed to build {Parallel HBK} oblique spaceships every 125906944 ticks. This gun was created by Chris Cain on 3 January 2015.parasiteA self-sustaining reaction attached to the output of a rake or puffer, that damages or modifies the standard output. Compare {tagalong}. In 2009, while experimenting with {novelty generator} patterns in {Golly}, Mitchell Riley discovered parasites on glider streams from p20 and p8 backward rakes. In some cases, parasites can even "reproduce", as in the pattern below, though the number of copies is limited since they will eventually use up their host glider stream:                                                           ! ! ! !!! " """ # # ######$$%% % %%%%%%%& &&&&&''' ' ''''''''''((( ((((((() ) ) )))))** * * ******+ + ++++ ,,-parentRA pattern is said to be a parent of the pattern it gives rise to after one generation. Some patterns have infinitely many parents, but others have none at all (see {Garden of Eden}). Typically parents are considered trivial if they contain groups of cells that can be removed without changing the result, such as isolated faraway cells. parent cells1The three cells that cause a new cell to be born.parityEven or odd, particularly as applied to the {phase} of an oscillator or spaceship. For example, in {slow salvo} constructions, the {intermediate target}s are frequently period 2, most often because they contain {blinker}s or {traffic light}s. A glider striking a P2 constellation will generally produce a different result depending on its parity. Period-4 intermediate targets are rare (or not used), so it doesn't matter for example whether an odd-parity glider in a slow salvo is phase 1 or phase 3. Only the even/odd parity is important.partial resultAn intermediate object found by a {search program} which might be a substantial part of a complete {spaceship} or {oscillator}, but which isn't complete. Running a partial result works for a few generations until the {speed of light} corruption from any unfinished edge destroys the whole object. But a partial result can still be used to see whether the object (if ever finished) would provide a desired {spark} or {perturbation}. If no partial results are found then it is likely that no such object exists under the constraints of the search. Very large partial results can indicate that there is a good chance that the object being searched for might actually exist (but this is no guarantee). Rerunning the search using the partial result as a base and relaxing some constraints, widening or adjusting the search area, or splitting the object into multiple {arm}s might result in finding a complete working object. As an example, here is a large partial result for a period 6 {knightship} found by Josh Ball in April 2017. The first 22 columns were rediscovered in 2018 as part of the successful search for {Sir Robin}. See also {almost knightship} for an earlier small example by Eugene Langvagen.                                        PD= {pentadecathlon} PD hassler= {p29 pentadecathlon hassler}PD-pair reflectorA pair of {pentadecathlon}s arranged so that their {V spark}s turn a glider by 90 degrees. The minimum {repeat time} is 45 ticks. This was found by Mark Niemiec on 6 January 1996, which is relatively recent considering how old {pentadecathlon} {technology} is./                pedestle1An {oscillator} found by Dave Buckingham in 1973.p54                      penny laneFound by Dave Buckingham, 1972.p4#           pentadecathlonFound in 1970 by Conway while tracking the history of short rows of cells, 10 cells giving this object, which is the most {natural} {oscillator} of period greater than 3. In fact it is the fifth most common {oscillator} overall, appearing in random soups slightly more frequently than the {clock}, but much less frequently than the {blinker}, {toad}, {beacon} or {pulsar}. The pentadecathlon can be constructed using just three gliders, as shown in {glider synthesis}. The pentadecathlon is the only known oscillator that has two {phase}s that are different {polyomino}es. It produces accessible {V spark}s and {domino} sparks, which give it a great capacity for doing {perturbation}s, especially for period 30 based {technology}. See {relay} for example.p15   pentant$Found by Dave Buckingham, July 1976.p5      pentapletAny 5-cell {polyplet}. pentapoleThe {barberpole} of length 5.p2 pentoadFound by Bill Gosper, June 1977. This is {extensible}: if an eater is moved back four spaces then another {Z-hexomino} can be inserted. (This extensibility was discovered by Scott Kim.)p5         pentominoAny 5-cell {polyomino}. There are 12 such patterns, and Conway assigned them all letters in the range O to Z, loosely based on their shapes. Only in the case of the {R-pentomino} has Conway's label remained in common use, but all of them can nonetheless be found in this lexicon.periodThe smallest number of generations it takes for an {oscillator} or {spaceship} to reappear in its original form. The term can also be used for a {puffer}, {wick}, {fuse}, {superstring}, stream of {spaceship}s, {factory} or {gun}. In the last case there is a distinction between {true} period and {pseudo} period. There is also a somewhat different concept of period for {wicktrailer}s.period doublerSee {period multiplier}.periodicFor {circuit} mechanisms, "periodic" is the opposite of {p1} or {stable}. Periodic {circuit}s necessarily contain {oscillator}s, and therefore they can generally only accept input {signal}s that are {synchronized} to the combined {period} of those oscillators (but see {universal regulator}). For {signal} {stream}s, "periodic" means that signals will only be present in the stream at one out of every n ticks, where n is the {period} of the stream. In a periodic {intermittent stream} there may be gaps, so that signals do not always appear at every nth tick. However, if a signal does appear, its distance measured in ticks from previous and future signals will always be an exact multiple of n.period multiplier`A term commonly used for a {pulse divider}, because dividing the number of {signal}s in a regular stream by N necessarily multiplies the {period} by N. The term "period multiplier" can be somewhat misleading in this context, because most such circuits can accept input streams that are not strictly {periodic}. Reactions have also been found to period double or period triple the output of some {rake}s to create high-period rakes in a relatively small space (i.e., an exponential increase in period for a linear increase in size). For {Herschel} signals and {glider gun}s, a number of small period doubler, tripler, and quadrupler mechanisms are known. For example, the following {conduit} produces one output glider after accepting four input {B-heptomino}es, or four Herschels if a conduit such as {F117} is prepended that includes the same {BFx59H} converter. See {semi-Snark} and {tremi-Snark} for additional examples using {glider} streams. As of June 2018 no stable period-multiplying {elementary conduit}s are known for a multiplication factor of five or higher, though it is easy to construct composite ones./      + , + , !"  !" - permanent switchA {signal}-carrying {circuit} that can be modified so that it cleanly absorbs any future signals instead of allowing them to pass. Optionally there may be a separate mechanism to restore the circuit to its original function. In the following example, a glider from the northeast (shown) will perform a simple {block pull} that switches off an {F166} conduit, so that any future Herschel inputs will be cleanly absorbed. A glider from the southwest (also shown) can restore the block to its original position.I233223""$   " #           5 6 5 6  0101"#9:#: !"789 7,-,- . / /!;"perpendicular grey ship= {against-the-grain grey ship}perturbTo change the fate of an object by reacting it with other objects. Typically, the other objects are sparks from {spaceship}s or {oscillator}s, or are {eater}s or impacting spaceships. Perturbations are typically done to turn a {dirty} reaction into a {clean} one, or to change the products of a reaction. In many desirable cases the perturbing objects are not destroyed by the reaction, or else are easily replenished. perturbation = {perturb}.PF35WOne of the three {elementary} conduits used in the composite {Fx176} {Herschel conduit}. It converts an input {pi-heptomino} into an output {wing} in 35 ticks. In November 2017, Aidan F. Pierce discovered the compact PF35W variant below, which improved the repeat time of the Fx176 to 73 ticks and allowed {glider}s from following {dependent conduit}s to escape freely: Several variants of the key catalyst are known, including {weld}ed additions for the Fx176 that absorb the following Herschel's first natural glider, since a standard fishhook eater doesn't quite fit. The following is a complete {Fx176} conduit incorporating the new PF45W:+                  phaseA representative generation of a periodic object such as an {oscillator} or {spaceship}. The number of phases is equal to the {period} of the object. The phases of an object usually repeat in the same cyclic sequence forever, although some {perturbation}s can cause a {phase change}. phase changeA {perturbation} of a periodic object that causes the object to skip forward or backward by one or more {phase}s. If the perturbation is repeated indefinitely, this can effectively change the {period} of the object. An example of this, found by Dean Hickerson in November 1998, is shown below. In this example, the period of the {oscillator} would be 7 if the {mold} were removed, but the period is increased to 8 because of the repeated phase changes caused by the mold's {spark}. The following pattern demonstrates a p4 c/2 {spaceship} found by Jason Summers, in which the phase is changed as it deletes a {forward glider}. This phase change allows the spaceship to be used to delete a glider wave produced by a {rake} whose period is 2 (mod 4). Phase changing reactions have enabled the construction of spaceships having periods that were otherwise unknown, and also allow the construction of period-doubling and period-tripling {convoy}s to easily produce very high period rakes. See also {blinker puffer}.(                 phase shift= {phase change}phiThe following common {spark}. The name comes from the shape in the generation after the one shown here. One {oscillator} which produces this spark is {Tanner's p46}. The {pentadecathlon} produces a slightly corrupted version of this spark. phi calculatorSee {pi calculator}. p1 circuitryphoenixAny pattern all of whose cells die in every generation, but which never dies as a whole. A {spaceship} cannot be a phoenix, and in fact every finite phoenix eventually evolves into an {oscillator}. The following 12-cell oscillator (found by the MIT group in December 1971) is the smallest known phoenix, and is sometimes called simply "the phoenix". This is {extensible} and is just the first of a family of phoenixes made by joining {component}s together to form a loop. Here is another member of this family. Every known phoenix oscillator has period 2. In January 2000, Stephen Silver showed that a period 3 oscillator cannot be a phoenix. The situation for higher periods is unknown. An easy {synthesis} of the phoenix is possible using four blocks as {seed}s. A {puffer} creating a growing row of phoenixes has the unusual property that the percentage of live cells that stay alive for more than one generation approaches zero. See {lone dot agar} for an example of an infinite phoenix. pi= {pi-heptomino}Pianola breederDA series of patterns by Paul Tooke in 2010, based on a simplification and extension of the {Gemini} spaceship's construction mechanism. Tooke produced a number of slow-salvo-constructed patterns with {superlinear growth}, including a series of breeder patterns of previously unknown types. For some patterns, the Gemini's two {construction arm}s were moved to a permanent stationary platform, using fourteen glider-loop channels instead of twelve. Some of these breeder patterns remain difficult to classify unambiguously. For example, one pattern was designed to be an MSS breeder - a modified {Gemini} spaceship puffing {slide gun}s which build lines of {block}s. However, the slide guns produce both moving and stationary objects at a linear rate, because streams of gliders are needed to reach out to the construction zone to do the {push} reaction and build more blocks. The pattern could therefore be classified as a hybrid MSM/MSS breeder. Other breeder patterns utilizing slide guns and {universal constructor} technology are likely to cause similar classification ambiguities. pi calculatorA device constructed by Adam P. Goucher in February 2010, which calculates the decimal digits of pi (the transcendental number, not the Life pattern!) and displays them in the Life universe as 8x10 dot matrix characters formed by arrangements of blocks along a diagonal stripe at the top. A {push} reaction moves a ten-block diagonal cursor to the next position as part of the "printing" operation for each new digit. The actual calculation is done in binary, using a streaming spigot algorithm based on linear fractional transformations. The pi calculator is made up of a 188-state computer connected to a printing device via period-8 {regulator}s and a binary-to-decimal conversion mechanism. The complete pattern can be found in {Golly}'s Very Large Patterns online archive, along with the very similar 177-state phi calculator which uses a simpler algorithm to calculate and print the Golden Ratio. p1 circuitry pi climberThe reaction that defines rate of travel of the {Caterpillar} spaceship. A pi climber consists of a pi-heptomino "climbing" a chain of blinkers, moving 17 cells every 45 ticks, and leaving behind an identical chain of blinkers, shifted downward by 6 cells. A single pi climber does not produce any gliders or other output, but two or more of them travelling on nearby blinker chains can be arranged to emit gliders every 45 ticks. Compare {Herschel-pair climber}.  pi-heptominoA common pattern. The name is also applied to later generations of this object. In a {pi ship}, for example, the pi-heptomino itself never arises.stabilizes at time 173pincers= {great on-off}pinwheel7Found by Simon Norton, April 1970. Compare {clock II}.p4#        pi orbitalFound by Noam Elkies, August 1995. In this {oscillator}, a {pi-heptomino} is turned ninety degrees every 42 generations. A second pi can be inserted to reduce the period to 84.p168C  &'2   &'13              1     1 2      . / 0 1 2    . / 1 2 8 9 18:568:5797#$%/158#&/28'/148#&48#$%85807-.01579-./01568: 018: 089 02  1    !!! ! ! ! !" "##$%%&& & &2&3&'' '2'3'(( ( ()***++++,, ,--- - - - -!-'-. . . . . .!.&.'.(.-.../ / /&/'/(/-/./ 0000 0!0"0$0*0.011 1!1,1-1.1/101212 2222&2-2.2/23233323 5!5*5+5 6#6$6%6&6'6(6+6!7"7)7*788 8+8,8-89!9#9(9*9-9: :%:&:+:,:;; pi portraitorQFound by Robert Wainwright in 1984 or 1985. Compare with {gourmet} and {popover}.p32w                                 pipsquirt= {pipsquirter} pipsquirter1An {oscillator} that produces a {domino} {spark} that is orientated parallel to the direction from which it is produced (in contrast to domino sparkers like the {pentadecathlon} and {HWSS}, which produce domino sparks perpendicular to the direction of production). See {p6 pipsquirter}, {p7 pipsquirter}.pi shipA {growing spaceship} in which the back part consists of a {pi-heptomino} travelling at a speed of 3c/10. The first example was constructed by David Bell. All known pi ships are too large to show here, but the following diagram shows how the pi fuse works.     pistonFound in 1971.p2      pi waveA line of {pi-heptomino}es stabilizing one another. For example, an infinite line of pi-heptominoes arranged as shown below produces a pi wave that moves at a speed of 3c/10 with period 30, and leaves no debris.$%&678$&68$&689pixel= {cell}plet = {polyplet} polyominolA finite collection of orthogonally connected cells. The mathematical study of polyominoes was initiated by Solomon Golomb in 1953. Conway's early investigations of Life and other cellular automata involved tracking the histories of small polyominoes, this being a reasonable way to ascertain the typical behaviour of different cellular automata when the patterns had to be evolved by hand rather than by computer. Polyominoes have no special significance in Life, but their extensive study during the early years lead to a number of important discoveries and has influenced the terminology of Life. (Note on spelling: As with "dominoes" the plural may also be spelt without an e. In this lexicon I have followed Golomb in using the longer form.) It is possible for a polyomino to be an {oscillator}. In fact there are infinitely many examples of such polyominoes, namely the {cross} and its larger analogues. The only other known examples are the {block}, the {blinker}, the {toad}, the {star} and (in two different phases) the {pentadecathlon}. A polyomino can also be a {spaceship}, as the {LWSS}, {MWSS} and {HWSS} show.polypletA finite collection of orthogonally or diagonally connected cells. This king-wise connectivity is a more natural concept in Life than the orthogonal connectivity of the {polyomino}.pondp1 pond on pondeThis term is often used to mean {bi-pond}, but may also be used of the following {pseudo still life}.p1 popoverWFound by Robert Wainwright in August 1984. Compare with {gourmet} and {pi portraitor}.p32                                              populationThe number of ON cells. P-pentomino>Conway's name for the following {pentomino}, a common {spark}.PPSNA pre-pulsar spaceship. Any of three different p30 c/5 orthogonal {spaceship}s in which a {pre-pulsar} is pushed by a pair of {spider}s. The back sparks of the spaceship can be used to perturb gliders in many different ways, allowing the easy construction of c/5 puffers. The first PPS was found by David Bell in May 1998 based on a p15 pre-pulsar spaceship found by Noam Elkies in December 1997. See also {SPPS} and {APPS}. The pattern below shows the basic mechanism of a PPS. The two isolated sparks at the left and right sides are the {edge spark}s from the two supporting spiders.c/5 orthogonallyp30           pre-beehive/The following common {parent} of the {beehive}. pre-blockRThe following common {parent} of the {block}. Another such pattern is the {grin}. precursor= {predecessor} predecessorLAny pattern that evolves into a given pattern after one or more generations. pre-pre-blockA common predecessor to the {pre-block} (and thus the {block}): This is easily created by a two-glider collision. Hitting the pre-pre-block with a glider can create a {MWSS}. Both of these reactions are shown below: pre-pulsarA common {predecessor} of the {pulsar}, such as that shown below. This duplicates itself in 15 generations. (It fails, however, to be a true {replicator} because of the way the two copies then interact.) A pair of {tub}s can be placed to eat half the pre-pulsar as it replicates; this gives the p30 oscillator {Eureka} where the pre-pulsar's replication becomes a movement back and forth. See {twirling T-tetsons II} for a variation on this idea. By other means the replication of the pre-pulsar can be made to occur in just 14 generations as half of it is eaten; this allows the construction of p28 and p29 oscillators. The pre-pulsar was also a vital component of the first known p26 and p47 oscillators. See also {PPS}. pre-pulsar spaceship= {PPS}.pressure cookerIFound by the MIT group in September 1971. Compare {mini pressure cooker}.p3!         primerA pattern originally constructed by Dean Hickerson in November 1991 that emits a stream of {LWSS}s representing the prime numbers. Some improvements were found by Jason Summers in October 2005.PRNG"= {pseudo-random number generator} propagator= {linear propagator}protein(Found by Dave Buckingham, November 1972.p3(                 pseudoOpposite of {true}. A {gun} emitting a period n {stream} of spaceships (or rakes) is said to be a pseudo period n gun if its mechanism oscillates with a period greater than n. This period will necessarily be a multiple of n. If the base mechanism's period is instead a fraction of n, then a {period multiplier} must also be present which is considered to be part of the mechanism, and the gun as a whole is still a true period gun. For example, a {filter} may be used on a lower-period gun to produce a compound gun such as the true {p48 gun}. Pseudo period n glider guns are known to exist for all periods greater than or equal to 14, with smaller periods being impossible. All known {p14 gun}s are pseudo guns requiring several {signal} {inject}ions, so they are quite large. The following smaller example is a pseudo period 123 gun, interleaving the streams from two true period 246 guns: The same distinction between true and pseudo also exists for {puffer}s.""#$ !%!#$&!$&$&'"$ "$!"$%                     ) * )')56'(5767878570146025123423%&'($%&'(*%(*)* ')    $ % 2 < = !!#!%!&!'!(!3!<!"#"'"("1"2"3":"<"####$#%#'#:#;#$$$$%$&$'$%%%%%&&'' (((( )))****0*1*++0+1+,,,,--.////0000011112223334>5pseudo-barberpoleFound by Achim Flammenkamp in August 1994. In terms of its minimum {population} of 15 this is the smallest known p5 {oscillator}. See also {barberpole}.p5      pseudo-random glider generatorA {pseudo-random number generator} in which the bits are represented by the presence or absence of {glider}s. The first pseudo-random glider generator was built by Bill Gosper. David Bell built the first moving one in 1997, using c/3 {rake}s.pseudo-random number generatorTA pseudo-random number generator (PRNG) is an algorithm that produces a sequence of bits that looks random (but cannot really be random, being algorithmically determined). In Life, the term refers to a PRNG implemented as a Life pattern, with the bits represented by the presence or absence of objects such as {glider}s or {block}s. Such a PRNG usually contains gliders or other {spaceship}s in a loop with a feedback mechanism that causes later spaceships to interfere with the generation of earlier spaceships. The {period} can be very high, as a loop of n spaceships has 2^n possible states.pseudo still lifeA {stable} pattern whose live cells are either immediately adjacent to each other, or are connected into a single group by adjacent dead cells where birth is suppressed by overpopulation. The definition of {strict still life} rules out such stable patterns as the {bi-block}. In such patterns there are dead cells which have more than 3 neighbours in total, but fewer than 3 in any component still life. These patterns are called pseudo still lifes, and have been enumerated up to 32 bits, as shown in the table below. Attribution of these counts is given in {strict still life}; see also {https://oeis.org/A056613}. The unique 32-bit {triple pseudo} still life is included in the last count in the table. As the number of bits increases, the pseudo still life count goes up exponentially by approximately O(2.56^n). By comparison, the rate for {strict still life}s is about O(2.46^n) while for {quasi still life}s it's around O(3.04^n). If a stable pattern's live cells plus its overpopulated dead cells do not form a single mutually adjacent group, the pattern is usually referred to as a {constellation}. It is also a {still life} in the general sense, but is neither "pseudo" nor "strict".puffer1An object that moves like a {spaceship}, except that it leaves debris behind. The first known puffers were found by Bill Gosper and travelled at c/2 orthogonally (see diagram below for the very first one, found in 1971). Not long afterwards c/12 diagonal puffers were found (see {switch engine}). Discounting {wickstretcher}s, which are not puffers in the conventional sense, no new velocity was obtained after this until David Bell found the first c/3 orthogonal puffer in April 1996. Other new puffer speeds followed over the next several years. Many spaceships that travel orthogonally at a speed less than c/2 have useful side or back {spark}s. These can be used to perturb {standard spaceship}s that approach from behind. A common technique for creating puffers for a new speed uses a {convoy} of the new spaceships to create debris from an approaching standard spaceship such that a new standard spaceship is recreated on the same path as the original one. This forms a closed loop, resulting in a high-period puffer for the new speed. As of June 2018, puffers have been found matching every known velocity of {elementary} spaceship, except for c/6 and c/7 diagonal and (2,1)c/6. It is also generally easy to create puffers based on {macro-spaceship}s, simply by removing some part of the trailing cleanup mechanism.,       puffer engineA pattern which can be used as the main component of a {puffer}. The pattern may itself be a puffer (e.g. the classic {puffer train}), it may be a spaceship (e.g. the {Schick engine}), or it may even be unstable (e.g. the {switch engine}). pufferfishA puffer discovered by Richard Schank in November 2014, from a symmetric soup search using an early version of {apgsearch}. It consists of a pair of {B-heptomino}es stabilised by a backend that leaves only pairs of blocks behind. It is simple enough to be easily synthesized with gliders. See {soup} for a random initial pattern, generated by {apgsearch} and recorded in {Catagolue}, that produces a pufferfish.c/2p12,                    pufferfish spaceship&Generally, any {spaceship} constructed using {pufferfish}. May refer specifically to the extensible c/2 {spaceship} constructed by Ivan Fomichev in December 2014, the first such spaceship to contain no period-2 or period-4 parts. (The first two or three rows might be considered to be period 2 or 4, but they are directly dependent on following rows for support.). The pattern consists of two adjacent {pufferfish} {puffer}s, plus four copies of a nontrivial period 36 c/2 {fuse} for pufferfish {exhaust}, discovered using a randomized soup search.c/2p361"*!"#)*+   !#)+,  !"$(*+    !"*+-   #%'),. $%'(,.     !#)+,- !"*+,      ! + , ,    , -    , - #$()#$().  -./ ,-/ ,-./+./ +0 *-/  )*./ ( $)*#$%&'("$&(012"%/#./13 puffer train>The full name for a {puffer}, coined by Conway before any examples were known. The term was also applied specifically to the classic puffer train found by Bill Gosper and shown below. This is very {dirty}, and the tail does not stabilize until generation 5533. It consists of a {B-heptomino} (shown here one generation before the standard form) escorted by two {LWSS}. (This was the second known puffer. The first is shown under {puffer}.) In April 2006, Jason Summers found a way to make the classic puffer train into a p20 {spaceship} by adding a {glider} at the back:   puff suppressorAn attachment at the back of a {line puffer} that suppresses all or some of its puffing action. The example below (by Hartmut Holzwart) has a 3-cell puff suppressor at the back which suppresses the entire puff, making a p2 {spaceship}. If you delete this puff suppressor then you get a p60 double {beehive} {puffer}. Puff suppressors were first recognised by Alan Hensel in April 1994.                                                                                   !pullA reaction, most often mediated by gliders, that moves an object closer to the source of the reaction. See {block pull}, {blinker pull}, {loaf pull}; also {elbow}.pulsarDespite its size, this is the fourth most common {oscillator} (and by far the most common of period greater than 2) and was found very early on by Conway. See also {pre-pulsar}, {pulsar quadrant}, and {quasar}.p30                  pulsar 18-22-20= {two pulsar quadrants}pulsar CP 48-56-72I= {pulsar} (The numbers refer to the populations of the three {phase}s.)Pulsar Pixel DisplayA large-scale raster line display device constructed by Mark Walsh in August 2010, where {pulsar}s form the individual pixels in an otherwise empty grid. The published sample pattern displays and erases eight 7x5-pixel characters on each of two lines of text. p30 circuitrypulsar quadrantThis consists of a quarter of the outer part of a {pulsar} stabilized by a {cis fuse with two tails}. This is reminiscent of {mold} and {jam}. Found by Dave Buckingham in July 1973. See also {two pulsar quadrants}.p3pulseA moving object, such as a {spaceship} or {Herschel}, which can be used to transmit information. See {pulse divider}. Also another name for a {pulsar quadrant}. pulse dividerxA mechanism that lets every n-th object that reaches it pass through, and deletes all the rest, where n > 1 and the objects are typically {glider}s, {spaceship}s or {Herschel}s. A common synonym is {period multiplier}. For n=2, the simplest known stable pulse dividers are the {semi-Snark}s. The following diagram shows a p5 glider pulse divider by Dieter Leithner (February 1998). The first glider moves the centre block and is reflected at 90 degrees. The next glider to come along will not be reflected, but will move the block back to its original position. The relatively small size and low period of this example made it useful for constructing compact glider {gun}s of certain periods, but it became largely obsolete with the discovery of the {stable} {CC semi-Snark}, which uses the same basic mechanism. Period 7, 22, 36 and 46 versions of this pulse divider are also known.O                             pulshuttle V7Found by Robert Wainwright, May 1985. Compare {Eureka}.p30     &' !$) !$) !$)  &'     & '     ! $ )  !$) !$)  &'  &' !$) !$) !$)  &'   *pure glider generatorA pattern that evolves into one or more {glider}s, and nothing else. There was some interest in these early on, but they are no longer considered important. Here's a neat example:     pushA reaction that moves an object farther away from the source of the reaction. See {sliding block memory}, {pi calculator}, {elbow}, {universal constructor}. See also {pull}, {fire}. pushalongAny {tagalong} at the front of a spaceship. The following is an example found by David Bell in 1992, attached to the front of a {MWSS}.      pyrotechnecium!Found by Dave Buckingham in 1972.p8(               pyrotechneczum]A common mistaken spelling of {pyrotechnecium}, caused by a copying error in the early 1990s.python= {long snake}Q = {Quetzal}qd$Abbreviation for {quarter diagonal}. Q-pentominoMConway's name for the following {pentomino}, a {traffic light} {predecessor}.quadjFound by Robert Kraus, April 1971. Of all {oscillator}s that fit in a 6x6 box this is the only {flipper}.p2QuadLife1A form of {colourised Life} in which there are four types of ON cell. A newly-born cell takes the type of the majority of its three {parent cells}, or the remaining type if its parent cells are all of different types. In areas where there are only two types of ON cell QuadLife reduces to {Immigration}.quadpoleThe {barberpole} of length 4.p2  quad pseudoA {still life} that can be broken down into four {stable} pieces but not into two or three. This term may refer to the following 34-bit pattern, found by Gabriel Nivasch in July 2001, or any similar pattern with the same property. As a consequence of the Four-Colour Theorem, there can be no analogous objects requiring decomposition into five or more pieces. By convention, patterns like this and the {triple pseudo} are considered to be {pseudo still life}s, not {strict still life}s. As of June 2018, it has been shown that no quad pseudo patterns exist with 32 or fewer bits, but a 33-bit pattern with this property may theoretically still be found."      quadratic filter&A {toolkit} developed by Dean Hickerson and Gabriel Nivasch in 2006, enabling the construction of patterns with asymptotic population growth matching an infinite number of different sublinear functions - namely, O(t^(1/2^n)) for any chosen n. See also {exponential filter}, {recursive filter}.quadratic growth8The fastest possible asymptotic rate of population growth for any Life pattern - O(t^2) in big-O notation, where t is the number of ticks. The first quadratic-growth pattern found was Bill Gosper's 1971 {breeder}. Many other types of breeders and {spacefiller}s have been constructed since. In April 2011, Stephen Silver gave an example of a one-cell-thick pattern over a million cells long that exhibited quadratic growth. In October 2015, Chris Cain constructed a one-cell-thick pattern with a reduced bounding box of 2596x1, improving on a series of previous longer results. The smallest known quadratic growth pattern by initial population is the 23-cell {switch-engine ping-pong} by Michael Simkin. There are an infinite number of possible growth rates between linear and quadratic growth. See {superlinear growth}.quadratic replicatorA pattern that fills all or part of the Life plane by making copies of itself in a nonlinear way. Small quadratic replicators are known in other Life-like rules, but as of July 2018 no example has been found or constructed in Conway's Life.quadratic sawtoothAny {sawtooth} pattern with a quadratic envelope, or specifically a pattern assembled by Martin Grant in May 2015, consisting of two {caber tosser}s with period multipliers for timing which activate and deactivate two toggleable rake guns (see {toggleable gun}). The gliders emitted by those rakes annihilate on the diagonal while the rakes are eaten by 2c/5 ships. All the rakes and gliders are destroyed before the next cycle. See also {Osqrtlogt}. quadri-SnarkA period-multiplying {colour-preserving} {signal} {conduit} found by Tanner Jacobi in October 2017, producing one output {glider} for every four input gliders. It is made by replacing one of the eaters in a {tremi-Snark} with a {catalyst} found using {Bellman}. The catalyst causes the formation of a {tub} which then requires an additional glider to delete. However, this adds 5 ticks to the repeat time, so that it becomes 48. If period quadrupling is needed with a {colour-changing} reaction, a {CP semi-Snark} and a {CC semi-Snark} can be used in series, or a period-multiplying {Herschel conduit} can be connected to a {syringe} and an appropriately chosen Herschel-to-glider {converter}.Z   )**(./()//12(),-/2( ) - / 0 -!,"-"3#4#%$3$5$&%5%$&%&&&5&7&8&+','2'3'5'7'+(,(2(3(5(7(5)7)8)"*#*2*3*4*5*8*!+#+2+6+7+!,4,5, -!-5-3.3/4/90quapole = {quadpole}quarter The following {spaceship}, found by Jason Summers in September 2000. The name is due to the 25-cell minimum population. This is the smallest known {c/4 spaceship} other than the {glider}. This spaceship can also be used to make the smallest known {tubstretcher}.c/4 diagonallyp4               quarter diagonal(A unit of measurement sometimes used for diagonal distances, especially for {slow salvo} glider {lane}s. One advantage of measurement in quarter diagonals is that gliders travel diagonally at 1qd/tick, so that the same integer value can serve as either a time or a diagonal distance measurement.quasarFound by Robert Wainwright, August 1971. This is related to the {pulsar}, and is just the smallest of an extensible series of p3 oscillators built using pulsar quadrants which are shifted with respect to each other. Here is the next oscillator in the series.p3                                                   quasi still lifeA {stable} {constellation} where the individual {still life}s share dead cells, so the neighborhoods of those dead cells are changed, but all cells that used to remain dead from under-population still do so. Under Life rules, this occurs when objects are diagonally adjacent (e.g., two {block}s sharing a single diagonal neighbor) or when single protruding cells in two objects such as {tub}s share multiple neighbors. The term is due to Mark Niemiec. As the number of bits increases, the quasi still life count goes up exponentially by approximately O(3.04^n), slightly more than a factor of three. By comparison, the rate for {strict still life}s is about O(2.46^n) while for {pseudo still life}s it's around O(2.56^n). queen beeSee {queen bee shuttle}.queen bee shuttleGFound by Bill Gosper in 1970. There are a number of ways to stabilize the ends. Gosper originally stabilized shuttles against one another in a square of eight shuttles. Two simpler methods are shown here; for a third see {buckaroo}. The queen bee shuttle is the basis of all known {true} p30 {gun}s (see {Gosper glider gun}).p30     queen bee shuttle pairAny arrangement of two {queen bee shuttle}s such that the two {beehive}s created between them are consumed in some way. There are many ways that the two shuttles can be placed, either head-to-head, or else at right angles. The most well-known and useful arrangement results in the {Gosper glider gun}. Other arrangements don't create any lasting output, but create large {spark}s which can perturb objects (especially gliders) in various ways. For example, one arrangement of a queen bee shuttle pair was used in the original {unit Life cell} as a {memory cell}. Here an input glider is converted into a block, which remains until it is deleted by a glider on a right-angled path. See {p690 gun} and {metamorphosis II} for two more examples.2                         QuetzalAny Herschel track-based gun with a period below 62, which is the lowest period with a stable glider-emitting conduit. This was Dieter Leithner's name for the {true} p54 glider gun he built in January 1998 - a short form of {Quetzalcoatlus}, which expresses the fact that the gun was a very large {Herschel loop} that was not an {emu}. Shortly afterwards Leithner also built a p56 Quetzal using a mechanism found by Noam Elkies for this purpose. In October 1998 Stephen Silver constructed a p55 Quetzal using Elkies' p5 {reflector} of the previous month. Quetzals of periods 57-61 have since been constructed. Some of the more recent Quetzals are not Herschel loops, but are instead short Herschel tracks firing several glider streams all but one of which is reflected back to the beginning of the track to create a new Herschel. Noam Elkies first had the idea of doing this for the p55 case, and Stephen Silver constructed the resulting gun shortly after building the original (much larger) p55 Quetzal. Jason Summers later built a p54 version, which is more complicated because the evenness of the period makes the timing problems considerably more difficult.QuetzalcoatlusA giant flying dinosaur after which Dieter Leithner named his p54 gun. Usually abbreviated to {Quetzal}, or simply Q (as in Q54, Q55, Q56, Q-gun, etc.).quilt= {squaredance}R= {R-pentomino}R190A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in July 1996. It is made up of two {elementary conduit}s, HRx131B + {BFx59H}. After 190 ticks, it produces a {Herschel} turned 90 degrees clockwise at (24, 16) relative to the input. Its {recovery time} is 107 ticks. A {ghost Herschel} in the pattern below marks the output location:K             !"$!#$    ###$%%%&R2D2This was found, in the form shown below, by Peter Raynham in the early 1970s. The name derives from a form with a larger and less symmetric {stator} found by Noam Elkies in August 1994. Compare with {Gray counter}.p8     r5= {R-pentomino}R64An {elementary conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in September 1995. After 64 ticks, it produces a {Herschel} rotated 90 degrees clockwise at (11, 9) relative to the input. Its {recovery time} is 153 ticks, though this can be improved to 61 ticks by adding a from-the-side eater inside the turn to avoid interference from the output Herschel's {first natural glider}, as shown below. A {ghost Herschel} in the pattern below marks the output location: R64 is one of the simplest known {Spartan} conduits, one of the two known {Blockic} conduits, and one of the few {elementary conduit}s in the original set of sixteen. See also {p256 gun}.8         rabbitsA 9-cell {methuselah} found by Andrew Trevorrow in 1986. The following {predecessor}, found by Trevorrow in October 1995, has the same number of cells and lasts two generations longer.stabilizes at time 17331  racetrackA pattern in which a {signal} makes its way in a loop through an "obstacle course" of reactions in order to demonstrate various ways that the signal can be reflected, temporarily stored, and converted. The more different reactions that are used the better the racetrack. David Goodenough built racetracks for p30 and p46 {technology} in 1995. Racetracks are also known for {Herschel conduit} {technology}, and simple ones are useful for building {oscillator}s and {glider gun}s.rakeUAny {puffer} whose debris consists of {spaceship}s. A rake is said to be forwards, backwards or sideways according to the direction of the spaceships relative to the direction of the rake. Originally the term "rake" was applied only to forwards c/2 glider puffers (see {space rake}). Many people prefer not to use the term in the case where the puffed spaceships travel parallel or anti-parallel to the puffer, as in this case they do not rake out any significant region of the Life plane (and, in contrast to true rakes, these puffers cannot travel in a stream, and so could never be produced by a {gun}). Although the first rakes (circa 1971) were c/2, rakes of other velocities have since been built. Dean Hickerson's construction of {Cordership}s in 1991 made it easy for c/12 diagonal rakes to be built, although no one actually did this until 1998, by which time David Bell had constructed c/3 and c/5 rakes (May 1996 and September 1997, respectively). Jason Summers constructed a 2c/5 rake in June 2000 (building on work by Paul Tooke and David Bell) and a c/4 orthogonal rake in October 2000 (based largely on reactions found by David Bell). The smallest possible period for a rake is probably 7, as this could be achieved by a 3c/7 orthogonal backwards glider puffer. The smallest period attained to date is 8 (Jason Summers' {backrake}, March 2001).$ratsFound by Dave Buckingham, 1972.p6        rattlesnake@Found by Dean Hickerson in January 2016 and named by Jeremy Tan.p11!                 R-beee= {bun}. This name is due to the fact that the pattern is a single-cell modification of a {beehive}.reaction envelopeThe collection of {cell}s that are alive during some part of a given active reaction. This term is used for {Herschel} {circuit}s and other stable circuitry, whereas {construction envelope} is specific to recipes in {self-constructing} circuitry. There are some subtleties at the edges of the envelope. Specifically, two reactions that have the exact same set of cells defining their envelopes may have different behavior when placed next to a single-cell protrusion like the tail of an {eater1}, or one side of a {tub}. The difference depends on whether two orthogonally adjacent cells at the edge of the envelope are ever simultaneously alive, within the protruding cell's {zone of influence}. reanimationA reaction performed by a {convoy} of {spaceship}s (or other moving objects) which converts a common stationary object into a glider without harming the convoy. This provides one way for {signal}s that have been frozen in place by some previous reaction to be released for use. Simple reactions using period 4 c/2 spaceships have been found for reanimating a {block}, {boat}, {beehive}, {ship}, {loaf}, {bi-block}, or {toad}. The most interesting of these is for a {beehive} since it seems to require an unusual p4 spaceship: Reanimation of a {loaf} is used many times in the {Caterloopillar}. It is also used in the {Caterpillar} as part of its {catch and throw} mechanism. Finally, reanimation can produce {rake}s from some {puffer}s. See {stop and restart} for a similar idea that applies to {Herschel conduit}s and other {signal} {circuit}ry. There are small objects which have no known reanimation reactions using c/2 ships other than the brute force method of hitting them with the output of {rake}s.c      !!! !    !                        "reburnable fuseA very rare type of {fuse} whose output is identical to its input, possibly with some spatial and/or temporal offset. See {lightspeed wire} for an example. Reburnable fuses are used primarily in the construction of fixed-speed {self-supporting} {macro-spaceship}s, where the speed of the fuse's burning reaction becomes the speed of the spaceship. Examples include the {Caterpillar}, {Centipede}, and {waterbear}.receiverSee {Herschel receiver}.recipe.= {glider synthesis} or {construction recipe}. recovery timeThe number of {tick}s that must elapse after a {signal} is sent through a {conduit}, before another signal can be safely sent on the same path. In general, a lower recovery time means a more useful conduit. For example, the {Snark}'s very low recovery time allowed for the creation of {oscillator}s with previously unknown {period}s, 43 and 53. For the most part this is a synonym for {repeat time}. However, {overclocking} a complex circuit can often allow it to be used at a {repeat time} much lower than its safe recovery time. rectifierThe smallest known 180-degree {reflector}, discovered by Adam P. Goucher in 2009. It was the smallest and fastest stable reflector of any kind until the discovery of the {Snark} in 2013. The rectifier has the same output glider as the {boojum reflector} but a much shorter {repeat time} of only 106 ticks. Another advantage of the rectifier is that the output glider is on a {transparent lane}, so it can be used in logic circuitry to merge two signal paths.E  "#!$'(!#("(*+ %&(* %(+ " ' * + "!#!$!%!&!$#%#'#$$&$'$%%%&',(recursive filterA {toolkit} developed by Alexey Nigin in July 2015, which enables the construction of patterns with population growth that asymptotically matches an infinite number of different superlinear functions. Toolkits enabling other, sublinear infinite series had been completed by Dean Hickerson and Gabriel Nivasch in 2006. See {quadratic filter} and {exponential filter}. Sublinear functions are possible using the recursive-filter toolkit as well. It can be used to construct a glider-emitting pattern with a slowness rate S(t) = O(log***...*(t)), the nth-level iterated logarithm of t, which asymptotically dominates any primitive-recursive function f(t). reflector Any {stable} or oscillating pattern that can reflect some type of {spaceship} (usually a {glider}) without suffering permanent damage. A pattern that is damaged or destroyed during the reflection process is generally called a {one-time} {turner} instead. The first known reflector was the {pentadecathlon}, which functions as a 180-degree glider reflector (see {relay}). Other examples include the {buckaroo}, the {twin bees shuttle} and some oscillators based on the {traffic jam} reaction. Glider {gun}s can also be made into reflectors, although these are mostly rather large. In September 1998 Noam Elkies found some fast small-period glider reflectors, with {oscillator}s supplying the required {domino} {spark}s at different periods. A {figure-8} produced a {p8 bouncer}, and a {p6 pipsquirter} produced an equivalent {p6 bouncer}. A more complicated construction allows a {p5 bouncer} (which, as had been anticipated, soon led to a {true} p55 {Quetzal} gun). And in August 1999 Elkies found a suitable {sparker} to produce a {p7 bouncer}, allowing the first p49 oscillator to be constructed. These were all called simply "p5 reflector", "p6 reflector", etc., until 6 April 2016 when Tanner Jacobi discovered an equally small and simple reaction, the {bumper}, starting with a {loaf} as {bait} instead of a {boat}. This resulted in a series of periodic {colour-preserving} reflectors, whereas Elkies' {bouncer} reflectors are all {colour-changing}. A useful mnemonic is that "bouncer" contains a C and is colour-changing, whereas "bumper" contains a P and is colour-preserving. Stable reflectors are special in that if they satisfy certain conditions they can be used to construct {oscillator}s of all sufficiently large periods. It was known for some time that stable reflectors were possible (see {universal constructor}), but no one was able to construct an explicit example until Paul Callahan did so in October 1996. Callahan's original reflector has a {repeat time} of 4840, soon improved to 1686, then 894, and then 850. In November 1996 Dean Hickerson found a variant in which this is reduced to 747. Dave Buckingham reduced it to 672 in May 1997 using a somewhat different method, and in October 1997 Stephen Silver reduced it to 623 by a method closer to the original. In November 1998 Callahan reduced this to 575 with a new initial reaction. A small modification by Silver a few days later brought this down to 497. In April 2001 Dave Greene found a 180-degree stable reflector with a repeat time of only 202 (see {boojum reflector}). This reflector won bounties offered by Dieter Leithner and Alan Hensel. Half of the prize money was recycled into a new prize for a small 90-degree reflector, which in turn was won by Mike Playle's {colour-preserving} {Snark} reflector. The Snark is currently the smallest known stable reflector, with a recovery time of 43. Playle has offered a $100 prize for a {colour-changing} stable reflector contained within a 25 by 25 {bounding box}, with a recovery time of 50 generations or less. As of June 2018, the following {splitter} is among the smallest known 90-degree {colour-changing} {reflector}s. The top output can be blocked off by an {eater} if needed. For small 180-degree colour-changing reflectors see {rectifier}, and also the sample pattern in {splitter}.u$%#&"$%&)*!#*!%&*,!"#$&+, $!% "&! % & 5 4 6 5        5656$45#%46#%6$ 6 7 !!!(!)!"("*"#*#*$+$8%!reflectorless rotating oscillatorA pattern that rotates itself 90 or 180 degrees after some number of {generation}s, with the additional constraint that multiple non-interacting copies of the pattern can be combined into a new oscillator with a period equal to the appropriate fraction of the component oscillators' period. The second constraint disqualifies small time-symmetric {oscillator}s such as the {blinker} and {monogram}. A working RRO might look something like a {pi orbital} or {p256 gun} loop containing one or more {pi}s or {Herschel}s in the same loop, but without any external stabilisation mechanism. Such patterns can be proven to exist (see {universal constructor}), but as of June 2018 none have been explicitly constructed in Life. There is no upper limit on {multiplicity} for a constructor-based RRO. regulatorAn object which converts input {glider}s aligned to some period to output gliders aligned to a different period. The most interesting case is a {universal regulator}, of which several have been constructed by Paul Chapman and others.relayVAny {oscillator} in which {spaceship}s (typically {glider}s) travel in a loop. The simplest example is the p60 one shown below using two {pentadecathlon}s. Pulling the pentadecathlons further apart allows any period of the form 60+120n to be achieved. This is the simplest proof of the existence of oscillators of arbitrarily large period. !"  #repeater Any {oscillator} or {spaceship}. repeat timeThe minimum number of generations that is possible between the arrival of one object and the arrival of the next. This term is used for things such as {reflector}s or {conduit}s where the {signal} objects ({glider}s or {Herschel}s, for example) will interact fatally with each other if they are too close together, or one will interact fatally with a disturbance caused by the other. For example, the repeat time of Dave Buckingham's 59-step B-heptomino to Herschel conduit (shown under {conduit}) is 58.rephaserThe following reaction that shifts the phase and path of a pair of gliders. There is another form of this reaction, {glider-block cycle}, that reflects the gliders 180 degrees. replicatoryA finite pattern which repeatedly creates copies of itself. Such objects are known to exist (see {universal constructor}), but no concrete example is known. The {linear propagator} may be considered to be the first example of a replicator built in Life, but this is debatable as each of its copies replicates itself only once, allowing no possibility of {superlinear growth}.reverse caber tosserLA storage mechanism for data feeding a {universal constructor} designed by Adam P. Goucher in 2018. A very large integer can be encoded in the position of a very faraway object. If the distance to that object is measured using {circuit}ry designed to be as simple as possible, a complete decoder and universal constructor can be created by colliding a small number of gliders - no more than 329 according to a June 2018 {glider synthesis}, and exactly 43 according to a July 1 redesign by Chris Cain using eight far-distant {GPSE}s and, amazingly, no stationary circuitry except for a single {catalyst} {block}. Some intermediate designs with 50+ gliders need no stationary circuitry at all. With the correct placement of the faraway object, the complete pattern is theoretically capable of building any glider-constructible object. This means that 43 is the maximum number of gliders required to build any constructible object, no matter what size. However, it is not possible to determine in practice what the locations of these 43 gliders should be, even for a relatively simple construction. reverse fuseiA {fuse} that produces some initial debris, but then burns {clean}ly. The following is a simple example.          revolverp2             RF28B}A {converter} with several known forms, many of which found by Dave Buckingham in 1972 and in the early 1980s. It accepts an {R-pentomino} as input and produces an output {B-heptomino} 28 ticks later. Of nine major variants known as of July 2018, four versions are shown below. For each version, the R-pentomino inputs are shown near the left and right edges, along with the B-heptomino output locations near the center. The version in the southeast is used in Paul Callahan's {Herschel receiver}. The one in the northwest is part of {L156}, but can be replaced by the variant in the northeast which produces a forward glider output.R# "$+#)*+(()%$%      % &       %$%%&!  " !!!!"!,"RF48HStephen Silver's alternate completion of Paul Callahan's {Herschel receiver}. As of June 2018 there are four known variants. The original version consists of a single {loaf}. A {ghost Herschel} marks the output location. Rich's p16A period 16 oscillator found by Rich Holmes in July 2016, using {apgsearch}. For its use as a {filter} see for example {p48 gun}."          ring of fireIThe following {muttering moat} found by Dean Hickerson in September 1992.p2                            !  !            "rleFRun-length encoded. Run-length encoding is a simple (but not very efficient) method of file compression. In Life the term refers to a specific ASCII encoding used for patterns in Conway's Life and other similar cellular automata. This encoding was introduced by Dave Buckingham and is now the usual means of exchanging relatively small patterns by email or in online forum discussions. As an example of the rle format, here is a representation of the {Gosper glider gun}. The "run lengths" are the numbers, b's are dead cells, o's are live cells, and dollar signs signal new lines: Over the years RLE format has been extended to handle patterns with multiple states, neighborhoods, rules, and universe sizes. A completely different encoding, {macrocell} format, is used for repetitive patterns that may have very large {population}s.2R-mangoA small active reaction, so named because it is a single-cell modification of a {mango}, but now more commonly known as {dove}. RNE-19T84mThe following {edge shooter} {converter}, accepting an input {R-pentomino} and producing a glider heading northeast (if the R-pentomino is in standard orientation). This converter has several common uses. It can be attached to the {L156} {Herschel conduit} to change it into a useful {period doubler}. Connecting it to the initial stage of the L156 produces a composite {Herschel-to-glider} converter often used as a {splitter}, or as a quasi-{edge shooter} after suppressing the additional glider output: The above H-to-2G mechanism appears in many places in the glider gun collection, for example, mainly for periods below 78 where {syringe}s can't be used to build small true-period guns. The insertion reaction allows a glider to be placed 19 ticks in front of another glider on the same lane, or 30 ticks behind it (28 if the perpendicular glider output is suppressed.),            rockDean Hickerson's term for an {eater} which remains intact throughout the eating process. The {snake} in Dave Buckingham's 59-step B-to-Herschel conduit (shown under {conduit}) is an example. Other still lifes that sometimes act as rocks include the {tub}, the {hook with tail}, the {eater1} (eating with its tail) and the {hat} (in Heinrich Koenig's stabilization of the {twin bees shuttle}). roteightorEFound by Robert Wainwright in 1972. See also {multiple roteightors}.p8#              rotorThe cells of an {oscillator} that change state. Compare {stator}. It is easy to see that any rotor cell must be adjacent to another rotor cell. R-pentominoThis is by far the most active {polyomino} with less than six cells: all the others stabilize in at most 10 generations, but the R-pentomino does not do so until generation 1103, by which time it has a {population} of 116, including six {glider}s. At generation 774, an R-pentomino produces a {queen bee} which lasts 17 more generations before being destroyed, enough time for it to flip over. This observation led to the discovery of the {Gosper glider gun}.RRO%= {reflectorless rotating oscillator}rule 22#Wolfram's rule 22 is the 2-state 1-D {cellular automaton} in which a cell is ON in the next generation if and only if exactly one of its three neighbours is ON in the current generation (a cell being counted as a neighbour of itself). This is the behaviour of Life on a cylinder of width 1.rulerA pattern constructed by Dean Hickerson in April 2005 that produces a stream of {LWSS} with gaps in it, such that the number of LWSS between successive gaps follows the "ruler function" (sequence A001511 in The On-Line Encyclopedia of Integer Sequences).rumbling riverAny {oscillator} in which the {rotor} is connected and contained in a strip of width 2. The following p3 example is by Dean Hickerson, November 1994.#%&  #$&  &()      !"#$%') %'./  !#')/  !%')+-.  !#)+     #$%&'(+-./0        ! " & + - 0     # ,     ! " 1 Rx202A {composite conduit}, one of the original sixteen {Herschel conduit}s, discovered by Dave Buckingham in May 1997. It is made up of two {elementary conduit}s, HR143B + {BFx59H}. After 202 ticks, it produces an inverted {Herschel} turned 90 degrees clockwise at (7, 32) relative to the input. Its {recovery time} is 201 ticks. A {ghost Herschel} in the pattern below marks the output location:g                      !!!"" # ##### $ $$$$%%%%&&&&'''(((()))))+++++++,,,--.. 4 4 4 5 6 67S:Usually means {big S}, but may sometimes mean {paperclip}.sailboatqA {boat} {hassle}d by a {Kok's galaxy}, a {figure-8} and two {eater3}s. Found by Robert Wainwright in June 1984.p16y                                     salvoYA collection of spaceships, usually gliders, all travelling in the same direction. Any valid glider construction {recipe} can be partitioned into no more than four salvos. Compare {flotilla}. In contrast with a {convoy}, the spaceships in a salvo are usually consumed by the reactions that they cause. Simple examples include {block pusher} and {block pull}. Salvos may be {slow} or {synchronized}. The following partially {synchronized} three-glider salvo produces an {LWSS} from a block. The above is a synchronized salvo and not a slow salvo, because the second glider must follow the first with the exact separation shown. The third glider can be considered to be a slow glider, because it will still delete the temporary loaf no matter how many {tick}s it is delayed. The {slow glider construction} entry includes an example of a true slow salvo.     sawtooth#Any finite pattern whose {population} grows without bound but does not tend to infinity. (In other words, the population reaches new heights infinitely often, but also infinitely often returns to some fixed value.) Conway's preferred plural is "sawteeth". The first sawtooth was constructed by Dean Hickerson in April 1991. The current smallest known sawtooth was found by a conwaylife.com forum user with the online handle 'thunk'. It has a bounding box of 74x60, and is the smallest known sawtooth in terms of its minimum repeating population of 177 cells. The following variant has a higher repeating population of 194 and an optimized bounding box of 62x56: Patterns combining a fast {puffer} with a slower {spaceship} have also been constructed (see {moving sawtooth}). See also {tractor beam}.568578    ,-56<=56<= + -  ) 8 9   % & ( * + 8 9 & ( ) ' !"!"$%$%","$*+,"#)    ) * !!!""""""###$$"$'$%% %!%'%&&& &!&"&&&(&'' '%'&'(')' ( ($(*( )') ***$*%*)***-&-......&.///%/000012222'2(233'3(344555 5666666!6"67 7>8SBM= {sliding block memory} Schick engineThis {spaceship}, found by Paul Schick in 1972, produces a large {spark} (the 15 live cells at the rear in the {phase} shown below) which can be {perturb}ed by other c/2 spaceships to form a variety of {puffer}s. See {blinker ship} for an example perturbation of the spark. The diagram below shows the smallest form of the Schick engine, using two {LWSS}. It is also possible to use two {MWSS}es or two {HWSS}es, or even an LWSS and an HWSS.c/2 orthogonallyp12(     Schick ship= {Schick engine}scorpionp1scrubberFound in 1971.p2        SE= {switch engine}sealRThe first diagonal {c/6 spaceship}, found by Nicolay Beluchenko in September 2005.c/6 diagonallyp6                                                !!!  !""#search programA computer program or script that automates the search for Life objects having certain desired properties. These are used because the difficulty of finding previously unknown Life objects now commonly exceeds the patience, speed, and accuracy of humans. Various types of search programs are used for finding objects such as {spaceship}s, {oscillator}s, {drifter}s, {catalyst}s, {soup}s, {Garden of Eden}s, and {slow salvo}s. Some search programs generate {partial result}s as they are running, so even if they don't complete successfully, something of use might still be salvaged from the run. Example search programs are {dr}, {lifesrc}, {gfind}, and {Bellman}. There are other types of programs which don't perform searches as such, but instead perform large constructions. These are used to correctly complete very complicated objects such as the {Caterpillar}, {Gemini}, {Caterloopillar}, and {universal constructor}-based spaceships such as the {Demonoid}s and {Orthogonoid}s.second glider domainThe second glider domain of an {edge shooter} is the set of spacetime offsets, relative to the {glider} {stream} emitted by the edge shooter, where a second independent glider stream may be present without interfering with the edge shooter. This is useful to know, because edge shooters are often used to generate glider streams very close to other glider streams, to make for example a {spaceship} {gun} or {converter}.second natural gliderThe glider produced at T=72 during the {evolution} of a {Herschel}. This is the common edge-shooting glider output used in the {NW31} converter and several other converter variants.seedA {constellation} of still lifes and/or oscillators, which can be converted into another Life object when it is struck by one or more gliders. Usually the resulting object is a rare still life or spaceship, more complex than the original constellation. {Spartan} single-glider (1G) seeds are more commonly seen than multi-glider seeds, because a Spartan 1G seed can be readily constructed and {trigger}ed using a {slow salvo}. See also {freeze-dried}. For example, the following is a 14{sL} 1G seed for a c/7 loafer spaceship.Y#""#$               -+,-**+  $$%%%%&&&''!("(!)"),,--..//.0Seeds of Destruction GameSAn interactive search application written by Paul Chapman in 2013. Its primary purpose was to assist in the design of self-destruct circuits in self-constructing circuitry. It has also regularly been helpful in completing glider syntheses, and was used to find the {31c/240} base reaction for the {shield bug} and {Centipede} spaceships.self-constructingA type of pattern, generally a {macro-spaceship}, that contains encoded construction information about itself, and makes a complete copy of itself using those instructions. The {Gemini}, {linear propagator}, {spiral growth} patterns, {Demonoid}s and {Orthogonoid} are examples of self-constructing patterns. Self-constructing spaceships often have trivially adjustable speeds. In many cases, the direction of travel can also be altered, less easily, by changing the encoded {construction recipe}. Compare {self-supporting}, {elementary}.self-supportingA type of pattern, specifically a {macro-spaceship}, that constructs {signal}s or {track}s or other scaffolding to assist its movement, but does not contain complete information about its own structure. Examples include the Caterpillar, {Centipede}, {half-baked knightship}, {waterbear}, and the {Caterloopillar}s. {Caterpillar} has been used as a general term for self-supporting spaceships, but it is not very appropriate for the HBKs. In general a self-supporting pattern cannot be trivially adjusted to alter its speed or direction. The variable speeds of the HBKs and the Caterloopillars are exceptions, but their direction of travel is fixed, and a specific Caterloopillar can't be made to change its speed without completely rebuilding it. Compare {self-constructing}, {elementary}. semi-cenarkkEither of two {semi-Snark} variants discovered by Tanner Jacobi in November 2017. The name is due to the initial {converter}, which produces a {century} output for every two input {glider}s. The minimum safe repeat time is 43 ticks for the smaller initial {catalyst} shown in {CC semi-cenark} and {CP semi-cenark}, or 42 ticks with the slightly larger catalyst variant shown below. There is also {overclocking} possible at period 36, 38, or 39. The reset glider can be followed immediately by a new trigger glider, as shown below, so the minimum repeat time for an {intermittent stream} of gliders is only 50 ticks.I        "# # !"  !!!!!! !" "#$ $$% semi-SnarkAny small {stable} {signal} {conduit} that produces one output glider for every two input gliders, with a 90 degree reflection. These can act as period-doublers for any glider stream whose period is at least equal to their repeat time, and so adding one of these to a single glider {gun} often results in a pattern much smaller than the older {technology} of crossing the output of two guns. The available semi-Snarks differ in their complexity, size, repeat time, and the colour of their output gliders. The {CC semi-Snark} was the first one found, and the term "semi-Snark" is often used specifically for this object. The "CC" prefix stands for {colour-changing}, by contrast with the more recently discovered {colour-preserving} {CP semi-Snark}. There are also CC and CP variants of a semi-Snark based on a two-{glider} to {century} {converter} discovered by Tanner Jacobi in November 2017. These {semi-cenark}s are the fastest semi-Snarks known as of July 2018, with a {repeat time} as low as 50 ticks, or a periodic input rate as low as 36 ticks. sesquihat(Halfway between a {hat} and a {twinhat}.p1 SGROAbbreviation for {stable} {glider} {reflector}. This term is no longer in use. shield bugUThe first 31c/240 {macro-spaceship}, constructed by Dave Greene on September 9, 2014.31c/240 orthogonallyp240 shillelaghp1ship The term is also used as a synonym of {spaceship}. A ship can be used as a {catalyst} in some situations. For example, it can suppress two of the {blinker}s from an evolving {traffic light}: It is also a one-glider {seed} for the {engine} of the {queen bee shuttle}:p1ship in a bottle7Found by Bill Gosper in August 1994. See also {bottle}.p16V                                  ship on boat= {ship tie boat} ship on ship = {ship-tie}ship-tie'The name is by analogy with {boat-tie}.p1  ship tie boatp1  short keysKFound by Dean Hickerson, August 1989. See also {bent keys} and {odd keys}.p3     shotgunA {gun} that fires a {salvo} of multiple {spaceship}s, almost always {glider}s, on parallel {lane}s. Two to four shotguns are often combined to turn a {glider synthesis} into a gun or {factory} for that synthesis.shoulderThe fixed upper end of a {construction arm}, generally consisting of one or more glider {gun}s or {edge shooter}s aimed at an {elbow} object.shuttleAny {oscillator} which consists of an active region moving back and forth between stabilizing objects. The most well-known examples are the {queen bee shuttle} (which has often been called simply "the shuttle") and the {twin bees shuttle}. See also {p54 shuttle}, {p130 shuttle} and {Eureka}. Another example is the p72 {R-pentomino} shuttle that forms part of the pattern given under {factory}.siameseA term used in naming certain {still life}s (and the {stator} part of certain {oscillator}s). It indicates that the object consists of two smaller objects sharing two or more cells. See {snake siamese snake} and {loaf siamese barge} for examples.sidePHalf a {sidewalk}. In itself this is unstable and requires an {induction coil}.sidecarkA small {tagalong} for an {HWSS} that was found by Hartmut Holzwart in 1992. The resulting {spaceship} (shown below) has a {phase} with only 24 cells, making it in this respect the smallest known spaceship other than the {standard spaceship}s and some trivial two-spaceship {flotilla}s derived from them. Note also that an HWSS can support two sidecars at once.       side-shooting gun = {slide gun} sidesnaggerLA {Spartan} eater found by Chris Cain in May 2015 with functionality similar to the {eater5}, as shown below. It has one {lane} less diagonal {clearance} on the high-clearance side than other eater5 variants, due to the presence of the boat. A good use of the sidesnagger can be seen in {p130 shuttle}. See also {highway robber}.              side-trackingSee {universal constructor}.sidewalkp1siesta7Found by Dave Buckingham in 1973. Compare {sombreros}.p52                       signaleMovement of information through the Life universe. Signals can be carried by {spaceship}s, {fuse}s, {drifter}s, or {conduit}s. Spaceships can only transfer a signal at the speed of the spaceship, while fuses can transfer a signal at speeds up to the {speed of light}. In practice, many signals are encoded as the presence or absence of a {glider} or other spaceship at a particular point at a particular time. Such signals can be combined by the collision of gliders to form logic operations such as AND, OR, and NOT gates. Signals can be duplicated using {glider duplicator}s or other {fanout} devices, and can be used up by causing {perturbation}s on other parts of the Life object. Signals are used in {Herschel conduit} circuitry, {universal constructor}s, {macro-spaceship}s, and other computational patterns such as the {pi calculator} and {Osqrtlogt} patterns. signal elbowA {conduit} with {signal} output 90 degrees from its input. This term is commonly used only for signal {wire}s, particularly {2c/3} signals. A {Snark} could reasonably be called a "glider elbow", but {glider reflector} is the standard term. A signal elbow with a {recovery time} less than 20 ticks would enable a trivial proof that Conway's Life is {omniperiodic}. A near miss is the following elbow-like {converter} found by Dean Hickerson. It successfully turns a 2c/3 signal by 90 degrees, but unfortunately changes it to a double-length signal in the process. This means that further copies of the converter can not be appended (e.g., to make a closed loop). Relatively small {composite} {MWSS} elbows can now be constructed, using Tanner Jacobi's 2015 discovery of a small {H-to-MWSS} component. For example, the {Orthogonoid} includes a constructor/reflector that reflects an MWSS stream by 180 degrees, but it can be trivially reconfigured to make a 90-degree MWSS elbow.  ! !                                                                             !! """""""""#####$$$$$$$$$%%%&&&&&&&'''(((((())))****++", Silver G-to-H5A variant of the {Silver reflector} made by substituting an {Fx119} conduit for the final {NW31}, allowing a Herschel output as well as the beehive-annihilating reset glider. It is still {Spartan}, and as long as the Fx119 is followed by a {dependent conduit}, it retains the faster 497-tick {recovery time}.Silver reflectorA {stable} {glider reflector} found by Stephen Silver in November 1998, by substituting an {NW31} converter for the second {Fx77} conduit in the {Callahan G-to-H} found a few days previous. The repeat time is 497 ticks:o                 !!----..../006777899%9&9::&:;&;(;<'<(<==<@=@<A=ACCDDDDEEHHIJJJJJKKLLLM2O3O2P3P>Q Silver's p5The following oscillator found by Stephen Silver in February 2000: As this has no {spark}, it appears useless. Nonetheless, in March 2000, David Eppstein found a way to use it to reduce the size of Noam Elkies' p5 {reflector}.p5    Simkin glider gunA {Herschel}-based glider gun discovered by Michael Simkin in April 2015. It consists of a Herschel running through two {B60} conduits. In terms of its 36-cell minimum population, it is one of the smallest known guns, sharing the record with the {Gosper glider gun}. In the double-barreled form, as well as the {pseudo}-period, {snake}-stabilized form shown below, it is the absolute record holder.p120#               ! single-armA type of {universal constructor} using just one construction arm and {slow salvo} techniques to construct, usually, {Spartan} or near-Spartan circuitry. Compare {two-arm}.single-channel1A type of {universal constructor} discovered and developed by Simon Ekstrom and others starting in December 2015. The initial {elbow operation} toolkit was near-minimal, with just one {push}, one {pull}, and one output glider of each colour (see {colour of a glider}). Later searches produced a much larger and more efficient library. Single-channel {recipe}s consist of a {stream} of {glider}s on a single {lane} and aimed at a {construction elbow}, usually separated from each other by at least 90 {tick}s. In spite of these strict limitations, single-channel recipes can be made to do surprising things. For example, it is possible to build a {Snark} directly on the {construction lane} of an active construction arm, starting from a single {elbow} {block}. This can allow the arm to reach efficiently around complex obstructions by bending itself through multiple {lossless elbow}s. Known recipes can also remove an elbow when it is no longer needed, by controlled demolition of the Snark. As of June 2018, almost all single-channel recipes are made up of {singleton}s and {synchronized} pairs of gliders, but no synchronized triplets or larger groups. This is not an inherent limitation of single-channel construction, but rather a limitation in the {search program} used to find currently known single-channel {toolkit}s. A useful byproduct of this limitation is that single-channel recipes can be trivially adjusted to allow them to safely cross perpendicular data streams, including other single-channel recipes (or earlier parts of the same recipe). To avoid collisions with a crossing stream, each singleton glider or glider pair can safely be delayed by any even number of ticks, or technically by any multiple of the period of the current {intermediate target}. The final result of the construction will not be affected.single-channel DemonoidSee {Demonoid}. single-lane= {single-channel}. singletonIn {single-channel} {recipe}s, a glider that is not {synchronized} with a neighboring glider in its {stream}. Compare {glider pair}.singular flip flop&Found by Robert Wainwright, July 1972.p2 sinking ship = {canoe} Sir Robinc/6, p6) The first elementary {knightship} in Conway's Game of Life, found by Adam P. Goucher on March 6, 2018, based on a partial by Tomas Rokicki.(2,1                                                       !!!!!!!"###$$%%%%%&&''''(((()))***+++++,,,,,------.../000122222334444445555556788888999999::::;;<===>>>??@@@@AAAABBBBBBCCCCDDDDEEFFFFGGGGHHHHHIIIIJJKMMNOsix Ls)This is a compact form of {loading dock}.p3 sixty-nine)Found by Robert Wainwright, October 1978.p4E                                           skewed quadp2skewed traffic light(Found by Robert Wainwright, August 1989.p3F                                                    sLtAbbreviation for {still life}, used most often in rough measurements of the complexity of a {Spartan} constellation. slide gunA {gun} which fires sideways from an extending arm. The arm consists of streams of {spaceship}s which are pushing a pattern away from the body of the gun and releasing an output spaceship every time they do so. Each output spaceship therefore travels along a different path. Dieter Leithner constructed the first slide gun in July 1994 (although he used the term "side shooting gun"). The following pattern shows the key reaction of this slide gun. The three gliders shown will push the block one cell diagonally, thereby extending the length of the arm by one cell, and at the same time they release an output glider sideways. (In 1999, Jason Summers constructed slide guns using other reactions.)    sliding block memoryaA memory register whose value is stored as the position of a {block}. The block can be moved by means of {glider} collisions. See {block pusher} for an example. In Conway's original formulation (as part of his proof of the existence of a {universal computer} in Life) two gliders were used to pull the block inwards by three diagonal spaces, as shown below, and thirty gliders were used to push it out by the same amount. Dean Hickerson later greatly improved on this, finding a way to pull a block inwards by one diagonal space using 2 gliders, and push it out the same distance using 3 gliders. In order for the memory to be of any use there also has to be a way to read the value held. It suffices to be able to check whether the value is zero (as Conway did), or to be able to detect the transition from one to zero (as Hickerson did). Dean Hickerson's sliding block memory is used in Paul Chapman's {URM}, and the key salvos from it are used in several other complex constructions, such as David Bell's {Collatz 5N+1 simulator} and Adam P. Goucher's {pi calculator} and {Spartan} {universal computer}-constructor.      slmakeA {search program} published by Adam P. Goucher in May 2017. It accepts as input a {constellation} of sufficiently widely separated {still life}s, and produces a {glider} {stream} that will perform a complete {slow glider construction} of that constellation, starting from a single block. One of slmake's primary uses is to make {self-constructing} patterns much easier to design and build. It is capable of finding {recipe}s not only for {Spartan} {stable} {circuit}ry, but also for other useful non-Spartan circuits such as {Snark}s, {syringe}s, and {H-to-MWSS} {converter}s, provided that they are separated from other nearby objects by a sufficient amount of empty space.slowSee {slow glider construction}. slow elbowA movable {construction elbow} that is controlled by a {slow salvo}, which most likely comes from a previous elbow in a multi-elbow {construction arm}. Unlike a standard elbow which is generally fixed on a single {construction lane} or at least within a narrow range, a slow elbow can move freely in two dimensions as long as there is room for it. Each slow elbow added to a construction arm results in an exponential increase in the cost (in gliders) of the final construction. Compare {lossless elbow}.slow glider constructionConstruction an object by a "slow salvo" of {glider}s all coming from the same direction, in such a way that timing of the gliders does not matter as long as they are not too close behind one another. This type of construction requires an initial seed object, such as a {block}, which is modified by each glider in turn until the desired object is produced. In May 1997, Nick Gotts produced a slow glider construction of a block-laying switch engine from a block, using a slow salvo of 53 gliders. Constructions like this are important in the study of {sparse Life}, as they will occur naturally as gliders created in the first few generations collide with {blonk}s and other debris. Slow glider constructions are also useful in some designs for {universal constructor}s. However, in this case the above definition is usually too restrictive, and it is desirable to allow constructions in which some gliders in the salvo are required to have a particular timing modulo 2 (a "p2 slow salvo"). This gives much greater flexibility, as {blinker}s can now be freely used in the intermediate construction steps. The {Snarkmaker} is a very large p2 slow salvo. A much smaller example is the following {edgy} construction of an {eater1} starting from a block. Adam P. Goucher's {slmake} {search program}, made available in May 2017, makes it much easier to find a slow glider construction for a wide variety of {stable} {circuit}ry.,     !""##%%%4%5%&3&4&'5'6( slow salvoSee {slow glider construction}. small fish= {LWSS} small lakewA 20-cell {still life}, but technically not actually a {lake} because it is not constructed entirely out of {domino}es.p1 smileyAFound by Achim Flammenkamp in July 1994 and named by Alan Hensel.p8 SMM breederSee {breeder}.smokeDebris that is fairly long-lived but eventually dies completely. Basically, a large {spark}. This term is used especially when talking about the output from a {smoking ship}. Some {Herschel conduit}s such as {Fx119} also create large amounts of smoke. smoking shipA {spaceship} which produces {smoke}. If the smoke extends past the edge of the rest of the spaceship, then it can be used to perturb other objects as the spaceship passes by. Running gliders into the smoke is often a good way to turn or duplicate them, or convert them into other objects. Sometimes the smoke from a smoking ship may itself be perturbed by accompanying spaceships in order to form a {puffer}. A simple example of a smoking ship is the {Schick engine}.snackerFound by Mark Niemiec in 1972. This is a {pentadecathlon} with stabilizers which force it into a lower period. The stabilizers make the {domino} spark largely inaccessible, but the snacker is {extensible}, as shown in the next diagram, and so a more accessible p9 domino spark can be obtained. In April 1998 Dean Hickerson found an alternative stabilizer that is less obtrusive than the original one, and this is also shown in this diagram. An end can also be stabilized by killer {candlefrobra}s.p9(            snailThe first known {c/5 spaceship}, discovered by Tim Coe in January 1996. For some time it was the slowest known orthogonal spaceship.c/5 orthogonallyp5 !  !  "#% $             $       " # %   ! !&snakep1 snake bitAn alternative name for a {boat-bit}. Not a very sensible name, because various other things can be used instead of a snake. A snake, or alternatively an {aircraft carrier}, is the smallest object that can consume a glider {stream} by effectively acting as an {eater} for every two incoming gliders. The one-cell reduction from the smallest real eater, the seven-cell {eater1}, has been important when trying to construct recent {sawtooth}s where the {population} must be minimized.snake bridge snakep1  snake dance%Found by Robert Wainwright, May 1972.p3  snake pitThis term has been used for two different {oscillator}s: the p2 snake pit (essentially the same as {fore and back}) and the p3 snake pit.snake siamese snakep1 SnarkA small stable 90-degree glider reflector with a repeat time of 43 ticks, discovered by Mike Playle on 25 April 2013 using a search utility he wrote called {Bellman}. Compare {boojum reflector}. Four common Snark variants are shown below: Playle's original at the top, and variants by Heinrich Koenig, Simon Ekstrom, and Shannon Omick to the left, bottom, and right, respectively. As of June 2018, only Playle's variant has a known {slow glider construction} {recipe} for all orientations.  % &   %   # % # $       .,-./0+1,-.1/12,-./2'(,01'(-.///12. / 1 2 &#'#&$'%(%)%&&)& '''' ((( ) )+,,,,,,------.......///////00011111222334 SnarkmakerYA {single-channel} {stream} of {glider}s that, when aimed to collide with an {elbow} {block} in a specific location, will perform a {slow glider construction} of a {Snark}, directly on the same {lane} as the incoming gliders. This allows a {construction arm} to add one or more {lossless elbow}s, so that it can bend around multiple corners without an exponential increase in construction cost. The Snarkmaker recipe used in the first single-channel {Demonoid}, {Orthogonoid}, and {spiral growth} patterns contains 2,254 gliders. This could be considerably reduced with a customized {search program}.SNG= {second natural glider}.SODGame= {Seeds of Destruction Game}sombrero$One half of {sombreros} or {siesta}. sombrerosFound by Dave Buckingham in 1972. If the two halves are moved three spaces closer to one another then the period drops to 4, and the result is just a less compact form of {Achim's p4}. Compare also {siesta}.p62                 soupA random initial pattern, either contained within a small area, or alternatively filling the whole Life universe. Finite soups probably have behaviors very different than infinite soups, but this is obviously unknown. Infinite soups may remain chaotic indefinitely since any reaction, no matter how rare, is bound to happen somewhere. Soups can have an average density, with results varying based on that. See {sparse Life} for a discussion of what can happen at a low density. Finite soups for sizes such as 16x16 (asymmetric) have been examined by the billions by scripts such as {apgsearch} to find interesting results. Many new {oscillator}s and {synthesis} {recipe}s have been discovered, as well as previously known rare patterns such as {stabilized switch engine}s. In addition, soups are used to generate statistical {census} data, and to decide whether specific objects can be considered {natural}. Soups can be fully random, or they can be forced to be {symmetric}. The results for these two types of soups can differ since symmetric soups tend to create large symmetrical objects at a much higher rate. Shown below is an unusual mirror-symmetric soup that produces a {pufferfish} and nothing else.                                                                                space dust2A part of a {spaceship} or {oscillator} which looks like a random mix of ON and OFF cells. It is usually very difficult to find a {glider synthesis} for an object that consists wholly or partly of space dust. As examples, the {295P5H1V1}, {fly}, and {seal} spaceships contain large amounts of space dust. spacefillerAny pattern that grows at a quadratic rate by filling space with an {agar}. The first example was found in September 1993 by Hartmut Holzwart, following a suggestion by Alan Hensel. The diagram below shows a smaller spacefiller found by Tim Coe. See also {Max}. Spacefillers can be considered as {breeder}s (more precisely, MMS breeders), but they are very different from ordinary breeders. The word "spacefiller" was suggested by Harold McIntosh and soon became the accepted term.                                                                    space nonfillerAny pattern that expands indefinitely to affect every cell in the Life plane, but leaves an expanding region of {vacuum} at its center. Compare {spacefiller}; see also {antstretcher}. The first nonfiller was discovered by Jason Summers on 14 April 1999:          !     !      "    ! " #       #    ! " #  !# #$"# !"!             % space rakeThe following p20 forwards glider {rake}, which was the first known rake. It consists of an {ecologist} with a {LWSS} added to turn the dying debris into {glider}s.A                      spaceship%Any finite pattern that reappears (without additions or losses) after a number of generations and displaced by a non-zero amount. By far the most {natural} spaceships are the {glider}, {LWSS}, {MWSS} and {HWSS}, followed by the {Coe ship} which has also evolved multiple times from random asymmetric {soup} starting conditions. See also the entries on individual spaceship speeds: {c/2 spaceship}, {c/3 spaceship}, {c/4 spaceship}, {c/5 spaceship}, {c/6 spaceship}, {c/7 spaceship}, {c/10 spaceship}, {c/12 spaceship}, {2c/5 spaceship}, {2c/7 spaceship}, {3c/7 spaceship}, {(2,1)c/6 spaceship}, and {17c/45 spaceship}. It is known that there exist spaceships travelling in all rational directions and at arbitrarily slow speeds (see {universal constructor}). Before 1989, however, the only known examples travelled at c/4 diagonally (gliders) or c/2 orthogonally (everything else). In 1989 Dean Hickerson started to use automated searches to look for new {elementary} spaceships, and had considerable success. Other people have continued these searches using tools such as {lifesrc} and {gfind}, and as a result we now have a great variety of elementary spaceships travelling at sixteen different velocities. The following table details the discovery of elementary spaceships with new velocities as of July 2018.Spaceships in Conway's Life#A series of articles posted by David Bell to the newsgroup comp.theory.cell-automata during the period August-October 1992 that described many of the new {spaceship}s found by himself, Dean Hickerson and Hartmut Holzwart. Bell produced an addendum covering more recent developments in 1996.spaghetti monsterThe first {3c/7 spaceship}, found by Tim Coe in June 2016. The spaceship travels orthogonally, has a minimum of 702 live cells and fits in a 27x137 bounding box.sparkA pattern that dies. The term is typically used to describe a collection of cells periodically thrown off by an {oscillator} or {spaceship}, but other dying patterns, particularly those consisting or only one or two cells (such as produced by certain glider collisions, for example), are also described as sparks. For examples of small sparks see {unix} and {HWSS}. Examples of much larger sparks are seen in {Schick engine} and {twin bees shuttle spark}. spark coilFound in 1971.p2sparkerAn {oscillator} or {spaceship} that produces {spark}s. These can be used to {perturb} other patterns without being themselves affected.sparking eaterOne of two {eater}s found in April 1997 and November 1998 by Dean Hickerson using his {dr} {search program}, shown below to the left and right respectively. These both absorb {glider}s as a standard eater does, but also produce separated single-bit {spark}s at the upper right, which can be used to delete antiparallel gliders with different phases as shown. The above mechanisms can be used to build {intermitting glider gun}s. The left-hand eater produces a spark nine ticks after a glider impact, with the result that the period of the constituent guns can't be a multiple of 4. The right-hand eater produces the same spark ten ticks after impact, which allows p4N guns to be used. The separation of the spark also allows this reaction to perform other {perturbation}s "around the corner" of some objects. For example, it was used by Jason Summers in 2004 to cap the ends of a row of ten {AK47 reaction}s to form a much smaller period 94 glider gun than the original one. (This is now made obsolete by the {AK94 gun}.)= !"  !# !      $ sparkyKA certain c/4 {tagalong}, shown here attached to the back of a {spaceship}.u                                        sparse LifeThis refers to the study of the evolution of a Life universe which starts off as a random {soup} of extremely low density. Such a universe is dominated at an early stage by {block}s and {blinker}s (often referred to collectively as {blonk}s) in a ratio of about 2:1. Much later it will be dominated by simple {infinite growth} patterns (presumably mostly {switch engine}s). The long-term fate of a sparse Life universe is less certain. It may possibly become dominated by self-reproducing patterns (see {universal constructor}), but it is not at all clear that there is any mechanism for these to deal with all the junk produced by switch engines.SpartanEA pattern composed of subunits that can be easily constructed in any orientation, usually with a {slow salvo}. Generally this means that the pattern is a {constellation} of Spartan still lifes: {block}, {tub}, {boat}, {hive}, {ship}, {loaf}, {eater1}, or {pond}. Other small objects may sometimes be counted as Spartan, including period-2 oscillators - mainly {blinker}s, but also {beacon}s or {toad}s, which may occur as {intermediate target}s in slow salvo {recipe}s. Most {self-constructing} patterns are Spartan or mostly Spartan, to simplify the process of self-construction. speed booster5Any mechanism which allows a {signal} (indicated by the presence or absence of a spaceship) to move faster than the spaceship could travel through empty space. The original speed booster is based on p30 {technology}, and is shown below: Here the top glider is boosted by passing through two {inline inverter}s, emerging 5 cells further along than the unboosted glider at the left. The fastest speed boosters are the {telegraph} and {p1 telegraph}, which can transfer a orthogonal signal at the {speed of light}, although their bit rate is rather slow. Diagonal speed boosters have also been built using {2c/3 wire}s or other stable components. See {stable pseudo-Heisenburp}. The {star gate} seems like it can transfer a signal faster than the {speed of light}. The illusion is explained in {Fast Forward Force Field}.g&'&'                          ! #$+,$+,  $   # !-speed of lightzThe greatest speed at which any effect can propagate; in {Life}, a speed of one cell per {generation}. Usually denoted c. S-pentomino@Conway's name for the following {pentomino}, which rapidly dies.spiderThis is the smallest known c/5 {spaceship}, and was found by David Bell in April 1997. Its side {spark}s have proved very useful in constructing c/5 {puffer}s, including {rake}s. See also {PPS}.c/5 orthogonallyp5L            spiral#Found by Robert Wainwright in 1971.p1 spiral growth]A {self-constructing} pattern built by Dave Greene in August 2014 that uses four {universal constructor}s (UCs) arranged in a diamond to build four more UCs in a slightly larger diamond. This was the first B3/S23 pattern that exhibited spiral growth. Much smaller versions have now been constructed using the {single-channel} construction toolkit.splitterNA {signal} {converter} that accepts a single input signal and produces two or more output signals, usually of the same type as the input. An older term for this is {fanout}, or "fanout device". A sub-category is the {one-time} splitter, which is not technically a converter because it can only be used once. One-time splitters are usually small {constellation}s that produce two or more {clean} gliders when struck by a single glider. In other words, they are multi-glider {seed}s. These are important for constructing self-destruct circuitry in {self-constructing} spaceships. The following combination, a {syringe} attached to an SE7T14 {converter} combined with an {NW31} converter, is one of the smallest known glider splitters as of July 2018. Another small splitter with a 90-degree {colour-changing} output is shown under {reflector}.]     $$%& ' &'     23234SPPSXThe symmetric {PPS}. The original PPS found by David Bell in May 1998. Compare {APPS}.c/5 orthogonallyp30sqrtgunAny glider-emitting pattern which emits its nth glider at a time asymptotically proportional to n^2. The first examples were constructed by Dean Hickerson around 1991. See also {quadratic filter}, {exponential filter}, {recursive filter}. squaredanceaThe p2 {agar} formed by tiling the plane with the following pattern. Found by Don Woods in 1971.squirter= {pipsquirter}S-spiral = {big S}stabilized switch engineA single {switch engine} which survives indefinitely by interacting with the appropriate {exhaust} such that it prevents the engine from ever being destroyed. The only known types of stabilized switch engines were found by Charles Corderman soon after he discovered the switch engine itself. There is a p288 block-laying type (the more common of the two) and the p384 glider-producing type. These two puffers are the most {natural} infinite growth patterns in Life. As of June 2018 they are the basis for every infinite growth pattern ever seen to occur from a random asymmetric {soup}, even after trillions of {census} results by {apgsearch} and similar projects. Patterns giving rise to block-laying switch engines can be seen under {infinite growth}, and one giving rise to a glider-producing switch engine is shown under {time bomb}. Here is the block-laying type showing its distinctive zig-zag trail of blocks.h         "#"#*+*+  ""##'$($'%(%#($(#)$):.;.:/;/223303130414,7-7,8-8&:':&;';<<stableA pattern is said to be stable if it is a {parent} of itself. Stable objects are oscillators with period 1 (p1), and are generally called {still life}s.stable pseudo-Heisenburp"A multi-stage {converter} constructed by Dave Greene in January 2007, using a complex recipe found by Noam Elkies to insert a signal into a {2c/3 wire}. The wire's high transmission speed allows a {signal} from a {highway robber} to catch up to a {salvo} of {glider}s. Ultimately the mechanism restores the key glider, which was destroyed by the highway robber in the first stage of the converter, to its exact original position in the salvo. Much smaller stable pseudo-Heisenburp devices have since been designed that use simple 0-degree glider {seed} {constellation}s instead of a 2c/3 wire. These patterns are labeled "pseudo-Heisenburp", because a true {Heisenburp device} does not even temporarily damage or affect a passing glider, yet can still produce an output {signal} in response. However, it is impossible to construct a {stable} device that can accomplish this for gliders. True stable Heisenburp devices are possible with many other types of {spaceship}s, but not with gliders which have no usable side {spark}s to initiate an output signal.staged recoveryA type of signal-processing {circuit} where the initial reaction between {catalyst}s an incoming signal results in an imperfect recovery. A catalyst is damaged, destroyed completely as in a {bait} reaction, or one or more objects are left behind that must be cleaned up before the circuit can be reused. In any of these three cases, output signals from the circuit must be used to complete the cleanup. In theory the cleanup process might itself be {dirty}, requiring additional cleanup stages. In rare cases this might theoretically allow the construction of special-purpose circuits with a lower {recovery time} than would otherwise be possible, but in practice this kind of situation does not commonly arise. An example is the record-breaking (at the time) 487-tick reflector constructed by Adam P. Goucher on 12 April 2009. 487 ticks was a slight improvement over the repeat time of the {Silver reflector}. The reflector featured a standard {Callahan G-to-H}, with cleanup by an internal {dirty} glider reflector found by Dieter Leithner many years before. This in turn was cleaned up by the usual ungainly Herschel plumbing attached to the G-to-H's output. The dirty glider reflector is not actually fully recovered before a second p487 signal enters the full reflector. However, it has been repaired by the time the internal reflector is actually needed again, so the cycle can be successfully repeated at p487 instead of p497.stairstep hexomino.The following {predecessor} of the {blockade}.stabilizes at time 63stamp collection)A collection of {oscillator}s (or perhaps other Life objects) in a single diagram, displaying the exhibits much like stamps in a stamp album. The classic examples are by Dean Hickerson (see {http://conwaylife.com/ref/DRH/stamps.html}). Many stamp collections contain "fonts" made of single cells (which cleanly die) to annotate the objects or to draw boxes around them. For example, here is a stamp collection which shows all the ways that two gliders can create a {loaf} or an {eater}: Alternatively, stamp collections can use {LifeHistory} for their annotations, but this requires a more sophisticated Life program to handle. Numbers, or more rarely letters, are sometimes constructed from stable components such as {block}s or {snake}s, but their readability is somewhat limited by placement constraints.j -, ,-.  () ')) - ,  ,-.      +*+  *,/standard spaceshipLA {glider}, {LWSS}, {MWSS} or {HWSS}. These have all been known since 1970.star)Found by Hartmut Holzwart, February 1993.p3$        star gateA device by Dieter Leithner (October 1996) for transporting a {LWSS} faster than the {speed of light}. The key reaction is the {Fast Forward Force Field}.statorThe cells of an {oscillator} that are always on. Compare {rotor}. (The stator is sometimes taken to include also some of those cells which are always off.) The stator is divided into the {bushing} and the {casing}. By analogy, the cells of an {eater} that remain on even when the eater is eating are considered to constitute the stator of the eater. This is not always well-defined, because an eater can have more than one eating action. statorless~A statorless {oscillator} is one in which no cell is permanently on - that is, the {stator} is empty, or in other words the oscillator has the maximum possible volatility. See the {volatility} entry for examples of this type of oscillator at different periods. Statorless oscillators can be constructed for any sufficiently large period, using {universal constructor} technology. statorless p5^Found by Josh Ball, June 2016. The first and only known {statorless} {period} 5 {oscillator}.p5D                               stepAnother term for a {generation} or {tick}. This term is particularly used in describing {conduit}s. For example, a 64-step conduit is one through which the active object takes 64 generations to pass. stillaterFound by Robert Wainwright, September 1985. This is one of only three essentially different p3 {oscillator}s with only three cells in the {rotor}. The others are {1-2-3} and {cuphook}.p3 still lifeFAny {stable} pattern, usually assumed to be finite and nonempty. For the purposes of enumerating still lifes this definition is, however, unsatisfactory because, for example, any pair of blocks would count as a still life, and there would therefore be an infinite number of 8-bit still lifes. For this reason a stricter definition is often used, counting a stable pattern as a {strict still life} only if its {island}s cannot be divided into two or more nonempty sets both of which are stable in their own right. If such a subdivision can be made, the pattern can be referred to as a {constellation}. If its cells form a single {cluster} it is also, more specifically, either a {pseudo still life} or a {quasi still life}. In rare cases above a certain size threshold, a pattern may be divisible into three or four stable nonempty subsets but not into two. See the 32-bit {triple pseudo} (32 bits) and the 34-bit {quad pseudo} for examples. All still lifes up to 18 bits have been shown to be {glider constructible}. It is an open question whether all still lifes can be incrementally constructed using glider collisions. For a subset of small still lifes that have been found to be especially useful in {self-constructing} circuitry, see also {Spartan}. The smallest still life is the {block}. Arbitrarily large still lifes are easy to construct, for example by extending a {canoe} or {barge}. The maximum density of a large still life is 1/2, which can be achieved by an arbitrarily large patch of {zebra stripes} or {chicken wire}, among many other options. See {density} for more precise limits.                                                                                                still life tagalonghA {tagalong} which takes the form of a {still life} in at least one {phase}. An example is shown below.@                  stop and goA pattern by Dean Hickerson in which a period 46 {shuttle} converts a glider into a block on one oscillation, and then converts the block back into a glider on the next oscillation. The glider is reflected back onto its own path, but with a delay.+(''()           * stop and restartA type of {signal} {circuit} where an input signal is converted into a stationary object, which is then re-activated by a secondary input signal. This can be used either as a memory device storing one bit of information, or as a simple delay mechanism. In the following January 2016 example by Martin Grant, a {ghost Herschel} marks the output signal location, and a "ghost {beehive}" marks the location of the intermediate still life. The {eater1} in the lower left corner catches the restart glider if no input signal has come in to create the beehive. This eater could be removed if it is useful to have both a "0" and a "1" output for a memory cell mechanism. The {catch and throw} {technology} in a {Caterpillar} is a somewhat similar idea. See also {stop and go} and {reanimation}._87789             "##$7$%5%6%7%$&%&5&'$'%'5'(()))**++,,--!-"-..!."/!0"0777788999999:::;streamA line of identical objects (usually {spaceship}s), each of which is moving in a direction parallel to the line, generally on the same {lane}. In many uses the stream is periodic. For example, the {new gun} produces a period 46 {glider} stream. The stream produced by a {pseudo-random glider generator} can have a very high period. Compare with {wave}. See also {single-channel} for a common use of non-periodic {glider} streams. stretcher_Any pattern that grows by stretching a {wick} or {agar}. See {wickstretcher} and {spacefiller}.strict still lifeA {still life} that is either a single connected {polyplet}, or is arranged such that a {stable} smaller pattern cannot be formed by removing one or more of its {island}s. For example, {beehive with tail} is a strict still life because it is connected, and {table on table} is a strict still life because neither of the {table}s are stable by themselves. See also {triple pseudo}, {quad pseudo}. Still lifes have been enumerated by Conway (4-7 bits), Robert Wainwright (8-10 bits), Dave Buckingham (11-13 bits), Peter Raynham (14 bits), Mark Niemiec (15-24 bits), and Simon Ekstrom and Nathaniel Johnston (25-32 bits). The resulting figures are shown below; see also {https://oeis.org/A019473}. The most recent search by Nathaniel Johnston has also confirmed that the {triple pseudo} pattern found by Gabriel Nivasch is the only such still life with 32 bits or less. It is therefore included in the pseudo still life count and not in the table below. As the number of bits increases, the strict still life count goes up exponentially by approximately O(2.46^n). By comparison, the rate for pseudo still life}s is about O(2.56^n) while for {quasi still life}s it's around O(3.04^n).!strict volatilityA term suggested by Noam Elkies in August 1998 for the proportion of cells involved in a period n {oscillator} which themselves oscillate with period n. For prime n this is the same as the ordinary {volatility}. Periods with known strictly-volatile oscillators include 1, 2, 3, 5, 6, 8, 13, 15, 22, 30, 33, and 177. Examples include {figure-8}, {Kok's galaxy}, {smiley}, and {pentadecathlon}. A composite example is the following p22, found by Nicolay Beluchenko on 4 March 2009:0                        super beehive = {honeycomb} superfountain A p4 {sparker} which produces a 1-cell spark that is separated from the rest of the oscillator by two clear rows of cells. The first superfountain was found by Noam Elkies in February 1998. In January 2006 Nicolay Beluchenko found the much smaller one shown below. See also {fountain}.p4g                                         superlinear growthGrowth faster than any rate proportional to T, where T is the number of ticks that a pattern has been run. This term usually applies to a pattern's population growth, rather than diametric growth or bounding-box growth. For example, {breeder}s' and {spacefiller}s' population asymptotically grows faster than any linear-growth pattern. It may also be used to describe the rate of increase in the number of subpatterns present in a pattern, such as when describing a {replicator}'s rate of reproduction. Due to limits enforced by the {speed of light}, no pattern's population can grow at an asymptotic rate faster than {quadratic growth}. See {switch-engine ping-pong} for the lowest-population superlinear growth pattern as of July 2018, along with a list of the record-holders. superstringAn infinite orthogonal row of cells stabilized on one side so that it moves at the {speed of light}, often leaving debris behind. The first examples were found in 1971 by Edward Fitzgerald and Robert Wainwright. Superstrings were studied extensively by Peter Rott during 1992-1994, and he found examples with many different periods. (But no odd periods. In August 1998 Stephen Silver proved that odd-period superstrings are impossible.) Sometimes a finite section of a superstring can be made to run between two tracks ("waveguides"). This gives a {fuse} which can be made as wide as desired. The first example was found by Tony Smithurst and uses {tub}s. (This is shown below. The superstring itself is p4 with a repeating section of width 9 producing one blinker per period and was one of those discovered in 1971. With the track in place, however, the period is 8. This track can also be used with a number of other superstrings.) Shortly after seeing this example, in March 1997 Peter Rott found another superstring track consisting of {boat}s. At present these are the only two waveguides known. Both are destroyed by the superstring as it moves along. It would be interesting to find one that remains intact. See {titanic toroidal traveler} for another example of a superstring. #'+/37;   "$&(*,.02468:< #'+/37;      #'+/37;   "$&(*,.02468:< #'+/37;=supportxThose parts of an object which are only present in order to keep the rest of the object (such an {engine} or an edge {spark}) working correctly. These can be components of the object, or else accompanying objects used to {perturb} the object. In many cases there is a wide variation of support possible for an engine. The {arm}s in many {puffer}s are an example of support.surprise(Found by Dave Buckingham, November 1972.p3$    SW1T43A {Herschel-to-glider} converter that produces a {tandem glider} useful in the {tee} reaction. It is classified as a "G3" converter because its two gliders are three {lane}s apart. Besides the southwest-travelling glider on lane 1, the converter also emits the Herschel's standard {first natural glider}, {SW-2}. The converter's full standard name is therefore "HSW1T43_SW-2T21". See {NW31} for an explanation of H-to-G naming conventions./                      SW-2The simplest type of {H-to-G} {converter}, where the converter's effect is simply to suppress a Herschel cleanly after allowing its {first natural glider} to escape. The name should be read as "SW minus two", where -2 is a glider {lane} number. The complete designation is SW-2T21. See {NW31T120} for a discussion of the standard naming conventions used for these converters. An unlimited number of converters have the SW-2T21 classification. The variants most often used consist of just one or two small {still life} {catalyst}s.C#$#!#!" (# $'$)$ % %(%)% & & '(')'(('()())))()******++*,SW-2T21= {SW-2}swanXA diagonal {spaceship} producing some useful sparks. Found by Tim Coe in February 1996.c/4 diagonallyp41                swimmer= {switch engine}. swimmer lane= {switch engine channel}.switchRA {signal}-carrying {circuit} that can send output signals to two or more different locations, depending on the state of the mechanism. These may be {toggle circuit}s, where the state of the switch changes after each use, or {permanent switch}es that retain the same state through many uses until a change is made with a separate signal.switchable gunA {gun} that includes a mechanism to turn the output stream off and on with simple signals, often gliders. A small example is Dieter Leithner's switchable LWSS gun from July 8, 1995. The ON signal enters from the northeast, and the OFF signal from the northwest:             -   , , - . $&$((0$)./01(-/12$(,/123<=$&-/12<=./010%%'- %&+,-**+()*()') !!!""##$%%%%%%!%"% &&&&&&&&& &"&%&'& '''''''''!'%')'((((()(/(0())))%)*)/)0)*)*%+)+%,',>- switch engineThe following pattern discovered by Charles Corderman in 1971, which is a {glide symmetric} unstable {puffer} which moves diagonally at a speed of c/12 (8 cells every 96 generations). The {exhaust} is {dirty} and unfortunately catches up and destroys the switch engine before it runs 13 full periods. Corderman found several ways to stabilize the switch engine to produce {puffer}s, using either one or two switch engines in tandem. See {stabilized switch engine} and {ark}. No {spaceship}s were able to be made from switch engines until Dean Hickerson found the first one in April 1991 (see {Cordership}). Switch engine {technology} is now well-advanced, producing many c/12 diagonal spaceships, puffers, and rakes of many periods. Small {polyomino}es exist whose {evolution} results in a switch engine. See {nonomino switch engine predecessor}. Several three-glider collisions produce {dirty} reactions that produce a stabilized switch engine along with other {ash}, making {infinite growth}. Until recently the only known syntheses for {clean} unstabilized switch engines used four or more gliders. There are several such recipes. In the reaction shown below no glider arrives from the direction that the switch engine will travel to, making it easier to repeat the reaction: Running the above for 20 ticks completes a {kickback} reaction with the top two gliders, resulting in the three-glider switch engine recipe discovered by Luka Okanishi on 12 March 2017.switch engine channelZTwo lines of {boat}s (or other suitable objects, such as {tub with tail}s) arranged so that a {switch engine} can travel between them, in the following manner: David Bell used this in June 2005 to construct a "bobsled" oscillator, in which a switch engine {factory} sends switch engines down a channel, at the other end of which they are deleted.!          switch engine chute= {switch engine channel}switch-engine ping-pongA very large (210515x183739) {quadratic growth} pattern found by Michael Simkin in October 2014. Currently this is the smallest starting population (23 cells) known to result in a quadratic population growth rate. Previous record-holders include {Jaws}, {mosquito1}, {mosquito2}, {mosquito3}, {mosquito4}, {mosquito5}, {teeth}, {catacryst}, {metacatacryst}, {Gotts dots}, {wedge}, {26-cell quadratic growth}, {25-cell quadratic growth}, and {24-cell quadratic growth}. symmetricUAny object which can be rotated and/or flipped over an axis and still maintain the same shape. Many common small objects such as the {block}, {beehive}, {pond}, {loaf}, {clock}, and {blinker} are symmetric. Some larger symmetric objects are {Kok's galaxy}, {Achim's p16}, {cross}, {Eureka}, and the {pulsar}. Large symmetric objects can easily be created by placing multiple copies of any finite object together in a symmetrical way. Unless the individual objects interact significantly, this is considered trivial and is not considered further here (e.g., two {LWSS}s travelling together a hundred cells apart). There are two kinds of symmetry. Odd symmetry occurs when an object's line of reflection passes through the center of a line of cells. Objects with odd symmetry have an odd number of columns or rows, and can have a {gutter}. Even symmetry occurs when the line of reflection follows the boundary between two lines of cells. Objects with even symmetry have an even number of columns or rows. Because the Life universe and its rules are symmetric, all symmetric objects must remain symmetric throughout their {evolution}. Most non-symmetric objects keep their non-symmetry as they evolve, but some can become symmetric, especially if they result in a single object. Here is a slightly more complicated example where two gliders interact to form a {blockade}: Many useful objects are symmetric along an orthogonal axis. This commonly occurs by placing two copies of an object side by side to change the behaviour of the objects due to the inhibition or killing of new cells at their {gutter} interface. Examples of this are {twin bees shuttle}, {centinal}, and the object shown in {puffer}. Other useful symmetric objects are created by perturbing a symmetric object using nearby {oscillator}s or {spaceship}s in a symmetric manner. Examples of this are {Schick engine}, {blinker ship}, and {hivenudger}. Many {spaceship}s found by {search program}s are symmetric because the search space for such objects is much smaller than for non-symmetrical spaceships. Examples include {dart}, {60P5H2V0}, and {119P4H1V0}.        synchronizedIndicates that precise relative timing is required for two or more input {signal}s entering a {circuit}, or two or more sets of {glider}s participating in a {glider synthesis}. Compare {asynchronous}. See also {salvo} and {slow glider construction}. synchronous= {synchronized} synthesis= {glider synthesis}syringeA small stable {converter} found by Tanner Jacobi in March 2015, accepting a glider as input and producing an output {Herschel} As of June 2018 it is the smallest known converter of this type, so it is very often used to handle input gliders in complex {signal} {circuit}ry, as described in {Herschel circuit}. A second glider can safely follow the first any time after 78 ticks, but {overclocking} also allows the syringe to work at a {repeat time} of 74 or 75 ticks. If followed by a {dependent conduit} a simple {eater2} can be used instead of the large {weld}ed {catalyst} shown here. A {ghost Herschel} marks the output location. A different version of the large catalyst, with better {clearance} for some situations, can be seen in the {switch} entry.M                    !!     "T= {T-tetromino}tableThe following {induction coil}.table on tablep1 tag = {tagalong}tagalong9An object which is not a {spaceship} in its own right, but which can be attached to one or more spaceships to form a larger spaceship. For examples see {Canada goose}, {fly}, {pushalong}, {sidecar} and {sparky}. See also {Schick engine}, which consists of a tagalong attached to two LWSS (or similar). The following {c/4 spaceship} (Nicolay Beluchenko, February 2004) has two wings, either of which can be considered as a tagalong. But if either wing is removed, then the remaining wing becomes an essential component of the spaceship, and so is no longer a tagalong.~ "        ! "    #   " # $ " # %  #&&  $%  $% %,-.  $%&- $'( %&')+,')-()-/ tail sparkA {spark} at the back of a spaceship. For example, the 1-bit spark at the back of a {LWSS}, {MWSS} or {HWSS} in their less dense phases.tameTo {perturb} a {dirty} reaction using other patterns so as to make it {clean} and hopefully useful. Or to make a reaction work which would otherwise fail due to unwanted products which interfere with the reaction.taming See {tame}. tandem gliderTwo gliders travelling on parallel lanes at a fixed spacetime offset, usually as a single signal in a {Herschel transceiver}. See also {glider pair}. Tanner's p46tAn {oscillator} found by Tanner Jacobi on 20 October 2017. This oscillator hassles an evolving {pi-heptomino} to produce an {phi} {spark}. The spark is very accessible and is able to perturb many things. The snakes can be replaced with eaters to form a slightly smaller version, as shown in the p46 MWSS gun in {gliderless} The period of this new oscillator is the same as the old {twin bees shuttle}, and so this is able to expand the known p46 {technology}. For example, a p46 glider gun can be made from a Tanner's p46 and just one of the {twin bees shuttle}s. Acting on their own, two copies of Tanner's p46 placed at right angles to each other with their sparks interacting can produce two different p46 glider guns and a gliderless p46 MWSS gun. See {p46 gun} and {gliderless} for two of these. These are the first p46 guns found which do not use a twin bees shuttle at all.p46)               targetA necessary component of a {slow salvo} recipe used by a {single-arm} {universal constructor}. A target usually consists of a single object, or sometimes a small {constellation} of common still lifes and/or oscillators. See {intermediate target}. If no {hand} target is available, a construction arm may be unable to construct anything, unless recipes are available to generate targets directly from the {elbow}.teardropThe following {induction coil}, or the formation of two beehives that it evolves into after 20 generations. (Compare {butterfly}, where the beehives are five cells further apart.)  technician'Found by Dave Buckingham, January 1973.p5!          technician finished product= {technician} technologyThe collective set of known reactions exploiting one subset of the Life universe. Examples of these subsets include {glider synthesis}, period 30 glider {stream}s, c/3 {spaceship}s, {sparker}s, {Herschel conduit}s, and {slow salvo}s. As new reactions and objects are found, over time any particular technology becomes more versatile and complete. Many Life experts like to concentrate on particular technologies.teepA head-on collision between three {glider}s, producing a perpendicular output glider that can be used to construct closely spaced glider {salvo}s, or to {inject} a glider into an existing {stream}. There are several workable {recipe}s. One of the more useful is the following, because the {tandem glider} can be generated by a small {Herschel} {converter}, {SW1T43}:      teethA 65-cell quadratic growth pattern found by Nick Gotts in March 2000. This (and a related 65-cell pattern which Gotts found at about the same time) beat the record previously held by {mosquito5} for smallest population known to have superlinear growth, but was later superseded by {catacryst}. See {switch-engine ping-pong} for the lowest-population {superlinear growth} pattern as of July 2018, along with a list of the record-holders. telegraph-A pattern created by Jason Summers in February 2003. It transmits and receives information using a rare type of {reburnable fuse}, a {lightspeed wire} made from a chain of beehives, at the rate of 1440 ticks per bit. The rate of travel of signals through the entire {transceiver} device can be increased to any speed strictly less than the {speed of light} by increasing the length of the beehive chain appropriately. "Telegraph" may also refer to any device that sends and receives lightspeed signals; see also {p1 telegraph}, {high-bandwidth telegraph}.ternary reaction'Any reaction between three objects. In particular, a reaction in which two gliders from one stream and one glider from a crossing stream of the same period annihilate each other. This can be used to combine two glider guns of the same period to produce a new glider gun with double the period.test tube babyp2 tetrapletAny 4-cell {polyplet}. tetrominoAny 4-cell {polyomino}. There are five such objects, shown below. The first is the {block}, the second is the {T-tetromino} and the remaining three rapidly evolve into {beehive}s. $% %&'#The Online Life-Like CA Soup SearchA distributed search effort set up by Nathaniel Johnston in 2009, using a Python script running in {Golly}. Results included a collection of the longest-lived 20x20 soups, as well as a {census} of over 174 billion {ash} objects. It has since been superseded by {Catagolue}.The Recursive Universe[A popular science book by William Poundstone (1985) dealing with the nature of the universe, illuminated by parallels with the game of Life. This book brought to a wider audience many of the results that first appeared in {LifeLine}. It also outlines the proof of the existence of a {universal constructor} in Life first given in {Winning Ways}.thumbA {spark}-like protrusion which flicks out in a manner resembling a thumb being flicked. Below on the left is a p9 thumb sparker found by Dean Hickerson in October 1998. On the right is a p4 example found by David Eppstein in June 2000.K                  thunderbirdstabilizes at time 243tick= {generation} tic tac toe= {octagon II}tieA term used in naming certain {still life}s (and the {stator} part of certain {oscillator}s). It indicates that the object consists of two smaller objects joined point to point, as in {ship tie boat}. time bombThe following pattern by Doug Petrie, which is really just a glider-producing {switch engine} in disguise. See {infinite growth} for some better examples of a similar nature.     titanic toroidal travelerThe {superstring} with the following repeating segment. The front part becomes p16, but the eventual fate of the detached back part is unknown. TL= {traffic light} T-nosed p4?Found by Robert Wainwright in October 1989. See also {filter}.p4#          T-nosed p5*Found by Nicolay Beluchenko in April 2005.p5           !"  #$       !#& $&'(          ! # &                      # $                ! "              ) T-nosed p6Found by Achim Flammenkamp in September 1994. There is also a much larger and fully symmetric version found by Flammenkamp in August 1994.p6,              toadFound by Simon Norton, May 1970. This is the second most common {oscillator}, although {blinker}s are more than a hundred times as frequent. See also {killer toads}. A toad can be used as a 90-degree {one-time} {turner}. The protruding cells at the edges can perturb some reactions by encouraging and then suppressing births on successive ticks. For example, a toad can replace the northwest eater in the {Callahan G-to-H} converter, allowing it to be packed one diagonal cell closer to other circuits.p2 toad-flipperA {toad} {hassler} that works in the manner of the following example. Two {domino} {sparker}s, here {pentadecathlon}s, apply their {spark}s to the toad in order to flip it over. When the sparks are applied again it is flipped back. Either or both domino sparkers can be moved down two spaces from the position shown and the toad-flipper will still work, but because of symmetry there are really only two different types. Compare {toad-sucker}.      toad-suckerA {toad} {hassler} that works in the manner of the following example. Two {domino} {sparker}s, here {pentadecathlon}s, apply their {spark}s to the toad in order to shift it. When the sparks are applied again it is shifted back. Either or both domino sparkers can be moved down two spaces from the position shown and the toad-sucker will still work, but because of symmetry there are really only three different types. Compare {toad-flipper}.       toaster$Found by Dean Hickerson, April 1992.p58                         toggleable gun{Any {gun} that can be turned off or turned on by the same external signal - the simplest possible switching mechanism. An input signal causes the gun to stop producing gliders. Another input signal from the same source restores the gun to its original function. Compare {switchable gun}. Here's a small example by Dean Hickerson from September 1996: In the figure above, glider B and an LWSS are about to send a glider NW. Glider A will delete the next glider after B, turning off the output stream. But if the device were already off, B wouldn't be present and A would instead delete the leading LWSS, turning the device back on.           !toggle circuitWAny signal-processing {circuit} that switches back and forth between two possible states or outputs. An early example is the {boat-bit}. More recent discoveries include the {semi-Snark}s, which alternate between reflecting and absorbing input {glider}s. The following B-to-G {converter} sends alternate glider outputs in opposite directions.j 12  ,-02 ,05    -./12345  /1   /1345   013656- . - . &'&'  /0 / 0 """ "&"'")"1"### # # #&#(#)#0#1#2# $ $ $/$0$3$7%TOLLCASS2Acronym for {The Online Life-Like CA Soup Search}.toolkitA set of Life reactions and mechanisms that can be used to solve any problem in a specific pre-defined class of problems: {glider} timing adjustment, {salvo} creation, {seed} construction, etc. See also {universal toolkit}, {technology}.torusAs applies to Life, usually means a finite Life universe which takes the form of an m x n rectangle with the bottom edge considered to be joined to the top edge and the left edge joined to the right edge, so that the universe is topologically a torus. There are also other less obvious ways of obtaining a toroidal universe. See also {Klein bottle}. Every object in a torus universe obviously either dies or becomes a {still life} or {oscillator}.total aperiodic$Any finite pattern which evolves in such a way that no cell in the Life plane is eventually periodic. The first example was found by Bill Gosper in November 1997. A few days later he found the following much smaller example consisting of three copies of a p12 {backrake} by Dave Buckingham.)()*'(*0'()/01().12678./058888( ) * 7 ( + ( ( ) &'(&)5&456&346&345'45#$%"#$%&"#$&'/09%&./01:. / 1 2 6 : 0!1!7!8!9!:!$%&&&&6&7&8&'''''''''8'((((8())7)$*%+,,!,%,--"-#-$-%-5-6-..2.3.4.6.7./2/3/4/5/6/30405022 33333333 4444445555555566678;9 T-pentomino]Conway's name for the following {pentomino}, which is a common {parent} of the {T-tetromino}.trackfA path made out of {conduit}s, often ending where it begins so that the active {signal} object is cycled forever, forming an {oscillator} or a {gun}. This term has also been used to refer to the {lane} on which a {glider} or {spaceship} travels. The concept is very similar, but a reference to a "track" now usually implies a non-trivial supporting conduit. tractor beamA stream of {spaceship}s that can draw an object towards the source of the stream. The example below shows a tractor beam pulling a {loaf}; this was used by Dean Hickerson to construct a {sawtooth}.F#$%& #'#,-  $'+,-.  *+-. +,/traffic circlep100 !"  ! #  #  ! "               +./ +,/!"#*+,-.  %%*+,-.%+,/+./!"#'(&'(% ' ( $!&!"""$"'"%#&# $$$$ %% &&& ''())**++++++,,,,--....////00 traffic jam[Any {traffic light} {hassler}, such as {traffic circle}. The term is also applied to the following reaction, used in most traffic light hasslers, in which two traffic lights interact in such a way as to reappear after 25 generations with an extra 6 spaces between them. See {traffic lights extruder} for a way to make this reaction {extensible}.          traffic light$A common formation of four blinkers.p2 traffic lights extruderA growing pattern constructed by Jason Summers in October 2006, which slowly creates an outward-growing chain of {traffic light}s. The growth occurs in waves which travel through the chain from one end to the other. It can be thought of as a complex {fencepost} for a {wick} that does not need a {wickstretcher}. The following illustrates the reaction used, in which a newly created traffic light at the left eventually pushes the rightmost one slightly to the right.7..   !"#. %*+,012 % %..   !"#.3 trans-beacon on tablep2 trans-boat with tailp1  transceiver= {Herschel transceiver}.trans-loaf with tailp1  transmitter= {Herschel transmitter}. transparentYIn signal circuitry, a term used for a {catalyst} that is completely destroyed by the passing signal, then rebuilt. Often (though not always) the active reaction passes directly through the area occupied by the transparent catalyst, then rebuilds the catalyst behind itself, as in the {transparent block reaction}. See also {transparent lane}.transparent block reactionA certain reaction between a block and a {Herschel} {predecessor} in which the block reappears in its original place some time later, the reaction having effectively passed through it. This reaction was found by Dave Buckingham in 1988. It has been used in some {Herschel conduit}s, and in the {gunstar}s. Because the reaction involves a Herschel predecessor rather than an actual Herschel, the following diagram shows instead a {B-heptomino} (which by itself would evolve into a block and a Herschel).     transparent debris effecteA mechanism where a {Herschel} or other active reaction completely destroys a {catalyst} in a particular location in a {conduit}. After passing through or past that location, the same reaction then recreates the catalyst in exactly its original position. This type of catalysis is surprisingly common in {signal} {circuit}ry. For an example, see {transparent block reaction}. The transparent object is most often a very common {still life} such as a block or beehive. Rarer objects are not unknown; for example, a transparent {loaf} was found by Stephen Silver in October 1997, in a very useful {elementary conduit} making up part of a {Herschel receiver}. However, not surprisingly, rarer objects are much less likely to reappear in exactly the correct location and orientation, so transparent reactions involving them are much more difficult to find, on average.transparent lane(A path through a signal-producing {circuit} that can be used to merge signal streams. The signal is usually a {standard spaceship} such as a {glider}. It can either be produced by the circuit, or it can come from elsewhere, passing safely through on the same {lane} without interacting with the circuit. A good example is the NW31 converter, which has two glider outputs on transparent lanes: The optional third output shown in {NW31} is non-transparent, because the upper {eater1} catalyst would get in the way of a passing glider on the same lane.         tremi-Snark3A {colour-preserving} period-multiplying {signal} {conduit} found by Tanner Jacobi on 7 September 2017, producing one output {glider} for every three input gliders. It uses the same block-to-pre-honeyfarm {bait} reaction as the {Snark}, and so has the same 43-{tick} {recovery time}. Compare {semi-Snark}.D     !!!!"""""""####$$$$$$$$$%&&&&&'''( trice tongsFound by Robert Wainwright, February 1982. In terms of its 7x7 {bounding box} this ties with {jam} as the smallest p3 {oscillator}.p3triggerA {signal}, usually a single {glider}, that collides with a {seed} {constellation} to produce a relatively rare still life or oscillator, or an output {spaceship} or other signal. The constellation is destroyed or damaged in the process; compare {circuit}, {reflector}. Here a pair of trigger gliders strike a {dirty} seed constellation assembled by Chris Cain in March 2015, to launch a three-engine {Cordership}: "Trigger" is also used when a spaceship reacts with another object to cause a reaction to occur whenever desired (but perhaps only at particular intervals). The object being triggered lies {dormant} until the reaction is required. All {turner}s and {freeze-dried} constellations are triggerable. In some cases the object is not destroyed so that the reaction can be repeated after some {repeat time}. See for example {converter} and {reflector}, and more specifically {MWSS out of the blue} and {queen bee shuttle pair}.G45014501()()34" 3 5 ! # / 0 4 6 " # . 0 5 / "456!#4"#5 !!""%&&'', ,-- - -.. . .3344556 : ; ; <<7=triominoEither of the two 3-cell {polyomino}es. The term is rarely used in Life, since the two objects in question are simply the {blinker} and the {pre-block}.triple catererOFound by Dean Hickerson, October 1989. Compare {caterer} and {double caterer}.p30                  triple pseudoThe following pattern, found by Gabriel Nivasch in July 2001. It is unique among 32-bit {still life}s in that it can be broken down into three {stable} pieces but not into two. The term may also refer to any larger {stable} pattern with the same property. See also {quad pseudo}.    tripletAny 3-cell {polyplet}. There are 5 such objects, shown below. The first two are the two {triomino}es, and the other three vanish in two generations.#  $%&tripoleThe {barberpole} of length 3.p2 tritoad'Found by Dave Buckingham, October 1977.p3<                             trivialA trivial period-N oscillator is one in which every cell oscillates at some smaller factor of N. See {omniperiodic}. For example, the joining of a period 3 and a period 4 {oscillator} as shown below creates a single object which is a trivial oscillator of period 12. However, there are trivial oscillators that meet this requirement, but may still be considered to be {non-trivial} because the different-period {rotor}s are not separated by {stator} cells. An example is Dean Hickerson's {trivial p6}. Conversely, there are oscillators formed by trivial combinations of high-period {gun}s or {sparker}s that are only technically non-trivial, because the lower-period components overlap but do not interact in any way. "Trivial" is also used to describe a {parent} of an object which has groups of cells that can be removed without changing the result, such as isolated faraway cells. For example, here is a trivial parent of a block.         trivial p6An {oscillator} found by Dean Hickerson in December 1994. Every cell has period less than 6, so this is a {trivial} oscillator. It is unusual because it has period-2 cells in contact with period-3 cells.p6|                                                    trombone slideRAn arrangement of four 90-degree {reflector}s that can be placed into the path of a {glider} so as to delay it by an adjustable number of generations, without changing its {lane}. More generally, any combination of {circuit}s may be referred to as a trombone slide, if the grouping can be moved as a single unit that functions as a 180-degree glider {reflector}. The smallest known trombone slides are made using {Snark}s. In the trombone slide shown below, sample input and output gliders are shown. The input glider will reach the same output location 128 generations sooner if the trombone slide is removed. If the top and left Snarks are moved together diagonally to the upper left by N cells, then the glider delay is increased by 8N generations since the glider has to travel N more cells in each direction. This sliding action gives the trombone slide its name. If only the final Snark is moved, then the output glider's path can be altered by a number of full diagonals. Trombone slides made of the same type of component cannot alter the glider path by half-diagonals, and can only change the timing by multiples of 8 generations. For other timing changes, different components are necessary. These may be stable like the {Silver reflector} or the {colour-changing} example shown in the {reflector} article, or periodic like the various {bumper}s.            -+,-**+./00/ !!'('(,()+-   ' ) + - !!! ! !$!'!)!+!-!.!"$"%"&"'")"*"-"###(#-#$$$$$$%$($*$+$,$$%%%)%*% ' ' (!( ) ) )))) )!)")#) ***$*+++ +!+$+,,",$,%,- -!-"-%-...#.$.// /!/"/"0"1$1%1!2"2$2%255555667777819trueOpposite of {pseudo}. A {gun} emitting a period n stream of {spaceship}s (or {rake}s) is said to be a true period n gun if its mechanism oscillates with period n. The same distinction between true and pseudo also exists for {puffer}s. An easy way to check that a gun is true period n is to stop the output with an {eater}, and check that the result is a period-n {oscillator}. True period n guns are known to exist for all periods greater than 61 (see {My Experience with B-heptominos in Oscillators}), but only a few smaller periods have been achieved, namely 20, 22, 24, 30, 36, 40, 44, 45, 46, 48, 50, and 54 through 61. See also {Quetzal} for the 54-61 range.$$ T-tetromino8The following common {predecessor} of a {traffic light}.tubp1tubber,Found by Robert Wainwright before June 1972.p30                      tubeaterA pattern that consumes the output of a {tubstretcher}. The smallest known tubeater was found by Nicolay Beluchenko (September 2005), and is shown below in conjunction with the smallest known tubstretcher.M                                      tubstretcherAny {wickstretcher} in which the wick is two diagonal lines of cells forming, successively, a {tub}, a {barge}, a {long barge}, etc. The first one was found by Hartmut Holzwart in June 1993, although at the time this was considered to be a boatstretcher (as it was shown with an extra cell, making the tub into a {boat}). The following small example is by Nicolay Beluchenko (August 2005), using a {quarter}. In October 2005, David Bell constructed an adjustable high-period diagonal c/4 {rake} that {burn}s tubstretcher wicks to create {glider}s, which are then turned and duplicated by {convoy}s of diagonal {c/4 spaceship}s to re-ignite the stabilized ends of the same wicks.                      tub with tailIThe following 8-cell {still life}. See {eater} for a use of this object.p1tugalong = {tagalong}tumblerrThe smallest known p14 {oscillator}. Found by George Collins in 1970. The oscillator generates {domino} {spark}s, but they are fragile and no use has been found for them to date. In each domino, one cell is "held" (remains alive) for two generations, the other for three. By contrast, useful domino sparks are usually alive for only one tick per oscillator {period}.p14 tumbling T-tetsonIA {T-tetromino} {hassle}d by two {figure-8}s. Found by Robert Wainwright.p8"     Turing machineSee {universal computer}.turnerA {one-time} {glider} {reflector}, or in other words a single-glider {seed} (the term is seldom or never used in relation to spaceships other than gliders). One-time turners may be 90-degree or 180-degree, or they may be 0-degree with the output in the same direction as the input. A reusable turner would instead be called a reflector. Shown on the top row below are the four 90-degree turner reactions that use common small {ash} objects: {boat}, {eater1}, {long boat}, and {toad}. Of the reactions on the first row, the glider output is the same {parity} for all but the long boat. The three still lifes are all {colour-changing}, but the {toad} happens to be a {colour-preserving} turner. The third row shows an {aircraft carrier} serving as a "0-degree turner" that is also colour-changing. Three of the simplest 180-degree turners are shown in the second row. The {Blockic} 180-degree turner is colour-preserving. The {long boat} and {long ship} are again colour-changing; this is somewhat counterintuitive as the output glider is on exactly the same {lane} as the input glider, but gliders travelling in opposite directions on the same lane always have opposite colours. Many small one-time turner {constellation}s have also been catalogued. The 90-degree two-block turner on the right, directly below the toad, is also colour-changing but has the opposite parity. A one-time turner reaction can be used as part of a glider {inject}ion mechanism, or as a switching mechanism for a {signal}. If a previous reaction has created the sacrificial object, then a later glider is turned onto a new path. Otherwise it passes through the area unaffected. This is one way to create simple switching systems or logic {circuit}s. An example is shown in {demultiplexer}.k. / -./ !123 "234  ! " . %&/ %&-./6767!"12!"12   $$%%&&8' turning toads&Found by Dean Hickerson, October 1989.p4 wickS#$*+ ")  %',.023   #$'*+.1467012346923689656:turtleA {spaceship} found by Dean Hickerson in August 1989 that produces a {domino} {spark} at the back. Hickerson used this spark to convert an approaching {HWSS} into a {loaf}, as part of the first {sawtooth}. (Also see {tractor beam}). The shape of the back end of the turtle is distinctive. Very similar but wider back ends have been found in other c/3 ships to produce period 9 and 15 {spaceship}s.c/3 orthogonallyp3,              twin bees shuttleFound by Bill Gosper in 1971, this was the basis of all known {true} p46 {gun}s, and all known p46 oscillators except for {glider} {signal} loops using {Snark}s, until the discovery of {Tanner's p46} in 2017. See {new gun} for an example. There are numerous ways to stabilize the ends, two of which are shown in the diagram. On the left is David Bell's {double block reaction} (which results in a shorter, but wider, shuttle than usual), and on the right is the stabilization by a single block. This latter method produces the very large {twin bees shuttle spark} which is useful in a number of ways. See {metamorphosis} for an example. Adding a symmetrically placed block below this one suppresses the spark. See also {p54 shuttle}.p46&            twin bees shuttle pairAny arrangement of two {twin bees shuttle}s such that they interact. There are many ways that the two shuttles can be placed, either head-to-head, or else at right angles. Glider guns can be constructed in at least five different ways. Here is one by Bill Gosper in which the shuttles interact head-to-head: For other examples, see {new gun}, {edge shooter}, {double-barrelled} and {natural Heisenburp}.&       / 0   / 0   1twin bees shuttle spark8The large and distinctive long-lived {spark} produced, most commonly, by the {twin bees shuttle}. It starts off as shown below. After 3 generations it becomes {symmetric} along the horizontal axis, after 9 generations it becomes symmetric along the vertical axis also, and finally dies after 18 generations. Since the spark is isolated and long-lived, there are many possible {perturbation}s that it can perform. One of the most useful is demonstrated in {metamorphosis} where a glider is converted into a {LWSS}. Another useful one can turn a {LWSS} by 90 degrees: twinhatSee also {hat} and {sesquihat}.p1  twin peaks = {twinhat}twirling T-tetsons IIPFound by Robert Wainwright. This is a {pre-pulsar} {hassle}d by {killer toads}.p608                           TWIT = {eater5}two-armThe type of {universal constructor} exemplified by the original {Gemini} spaceship, where two independently programmed {construction arm}s sent gliders in pairs on 90-degree paths to collide with each other at the construction site. Construction recipes for two-arm constructors are much more efficient in general, but they require many more {circuit}s and multiple independent data streams, which both tend to increase the complexity of {self-constructing} circuitry. Compare {single-arm}. two-bit spark = {duoplet}. two eaters%Found by Bill Gosper, September 1971.p3 two pulsar quadrants?Found by Dave Buckingham, July 1973. Compare {pulsar quadrant}.p3 UC= {universal constructor}.underpopulation\Death of a cell caused by it having fewer than two {neighbour}s. See also {overpopulation}. unit cell= {unit Life cell}.unit Life cell A rectangular pattern, of size greater than 1x1, that can simulate Life in the following sense. The pattern by itself represents a dead Life cell, and some other pattern represents a live Life cell. When the plane is tiled by these two patterns (which then represent the state of a whole Life universe) they evolve, after a fixed amount of time, into another tiling of the plane by the same two patterns which correctly represents the Life generation following the one they initially represented. It is usual to use the prefix "meta-" for simulated Life features, so, for example, for the first known unit Life cell (constructed by David Bell in January 1996), one metatick is 5760 {tick}s, and one {metacell} is 500x500 cells. Capital letters were originally used to make this distinction - e.g., Generation, Cell - but this usage is no longer common. In December 2005, Jason Summers constructed an analogous unit cell for Wolfram's Rule 110, a one-dimensional {cellular automaton} that is known be universal. See also {OTCA metapixel}, {p1 megacell}. universalGSee {universal computer}, {universal constructor}, {universal toolkit}.universal computerA computer that can compute anything that is computable. (The concept of computability can be defined in terms of Turing machines, or by Church's lambda calculus, or by a number of other methods, all of which can be shown to lead to equivalent definitions.) The relevance of this to Life is that both Bill Gosper and John Conway proved early on that it is possible to construct a universal computer in the Life universe. (To prove the universality of a {cellular automaton} with simple rules was in fact Conway's aim in Life right from the start.) Conway's proof is outlined in {Winning Ways}, and also in {The Recursive Universe}. Until recently, no universal Life computer had ever been built in practice In April 2000, Paul Rendell completed a Turing machine construction (see {http://rendell-attic.org/gol/tm.htm} for details). This, however, has a finite tape, as opposed to the infinite tape of a true Turing machine, and is therefore not a universal computer. But in November 2002, Paul Chapman announced the construction of a universal computer, see {http://www.igblan.free-online.co.uk/igblan/ca/}. This is a universal register machine based around Dean Hickerson's {sliding block memory}. In 2009 Adam P. Goucher constructed a programmable {Spartan} universal computer/constructor pattern using stable {Herschel} circuitry. It included memory tapes and registers capable of holding a simple universal instruction set and program data, and also a minimal {single-arm} universal constructor. Its size meant that it was extremely impractical to program it to be {self-constructing}, though this was theoretically possible if the escape of large numbers of gliders could be allowed as a side effect. In February 2010, Paul Rendell completed a universal Turing machine design with an unlimited tape, as described in his thesis at {http://eprints.uwe.ac.uk/22323/1/thesis.pdf}. In 2016 Nicolas Loizeau ("Coban") completed a Life pattern emulating a complete 8-bit programmable computer. See also {universal constructor}.universal constructor A pattern that is capable of constructing almost any pattern that has a {glider synthesis}. This definition is a bit vague. A precise definition seems impossible because it is not known, for example, whether all {still life}s are constructible. In any case, a universal constructor ought to be able to construct itself in order to qualify as such. An outline of Conway's proof that such a pattern exists can be found in {Winning Ways}, and also in {The Recursive Universe}. The key mechanism for the production of gliders with any given path and timing is known as side-tracking, and is based on the {kickback reaction}. A universal constructor designed in this way can also function as a universal destructor: it can delete almost any pattern that can be deleted by gliders. In May 2004, Paul Chapman and Dave Greene produced a prototype programmable universal constructor. This is able to construct objects by means of {slow glider construction}s. It likely that it could be programmed to construct itself, but the necessary program would be very large; moreover an additional mechanism would be needed in order to copy the program. A universal constructor is theoretically most useful when attached to a {universal computer}, which can be programmed to control the constructor to produce the desired pattern of gliders. In what follows I will assume that a universal constructor always includes this computer. The existence of a universal constructor/destructor has a number of theoretical consequences. For example, the constructor could be programmed to make copies of itself. This is a {replicator}. The constructor could even be programmed to make just one copy of itself translated by a certain amount and then delete itself. This would be a (very large, very high period) {spaceship}. Any translation is possible, so that the spaceship could travel in any direction. If the constructor makes a rotated but unreflected copy of itself, the result would be a looping spaceship or {reflectorless rotating oscillator}. The constructor could also travel slower than any given speed, since we could program it to perform some time-wasting task (such as repeatedly constructing and deleting a block) before copying itself. Of course, we could also choose for it to leave some debris behind, thus making a {puffer}. It is also possible to show that the existence of a universal constructor implies the existence of a {stable} {reflector}. This proof is not so easy, however, and is no longer of much significance now that explicit examples of such reflectors are known. Progressively smaller universal-constructor mechanisms without an attached universal computer have been used in the {linear propagator}, {spiral growth} pattern, and the {Demonoid}s and {Orthogonoid}. See also {single-channel}. Another strange consequence of the existence of universal constructors was pointed out by Adam P. Goucher and Tanner Jacobi in 2015. Any glider-constructible pattern, no matter how large, can be constructed with a fixed number of gliders, by working out a construction recipe for a universal constructor attached to a decoder that measures the distance to a faraway object. The object's position encodes a numeric value that can be processed to retrieve as many bits of information as are needed to build a {slow salvo} to construct any given target pattern. The simplest design, requiring less than a hundred gliders, is described in {reverse caber tosser}.universal destructorSee {universal constructor}.universal register machine= {URM}universal regulator?A {regulator} in which the incoming gliders are aligned to period 1, that is, they have arbitrary timing (subject to some minimum time required for the regulator to recover from the previous glider). Paul Chapman constructed the first universal regulator in March 2003. It is adjustable, so that the output can be aligned to any desired period. A {stable} universal regulator was constructed by Dave Greene in September 2015, with a minimum delay between test signals of 1177 ticks. Later stable versions have reduced the delay to 952 ticks. A universal regulator can allow two complex {circuit}s to interact safely, even if they have different base {period}s. For example, signals from a {stable} logic circuit could be processed by a period-30 mechanism, though the precise timing of those signals would change in most cases.universal toolkit A set of Life reactions and mechanisms that can be used to construct any object that can be constructed by glider collisions. Different universal toolkits were used to construct the {linear propagator}, {10hd Demonoid}, {0hd Demonoid}, and {Orthogonoid}, for example.universe@The topology of the cells in the Life grid. In the normal universe (the usual {Life} arena), the grid is infinite in both directions. In a cylindrical universe, the grid is finite in one direction, and the cells at the two edges are adjacent to each other. In a {torus} universe, the grid is finite in both directions, and the cells at the top and bottom edges are adjacent, and the cells at the left and right edges are adjacent. There are several other more obscure types of universe. Objects found in the cylindrical and toroidal universes can also run in the normal universe if an infinite number of copies are arranged to support each other. Sometimes the objects can be supported in other ways to make a useful finite object. This is one reason that {soup} searches are run in alternative universes, to find such objects.unixTwo {block}s eating a {long barge}. This is a useful {sparker}, found by Dave Buckingham in February 1976. The name derives from the fact that it was for some time the mascot of the Unix lab of the mathematics faculty at the University of Waterloo.p6 unknown fateAn object whose {fate} is in some way unanswerable with our current knowledge. The simplest way that the fate of an object can be unknown involves the question of whether or not it exhibits infinite growth. For example, the fate of the {Fermat prime calculator} is currently unknown, but its behaviour is otherwise predictable. A different type of unknown fate is that of the {Collatz 5N+1 simulator}, which may become stable, or an oscillator, or have an indefinitely growing bounding box. Its behavior is otherwise predictable, and unlike the Fermat prime calculator the population is known to be bounded. Life objects having even worse behaviour (e.g. {chaotic growth}) are not known as of July 2018.up boat with tail= {trans-boat with tail} U-pentomino@Conway's name for the following {pentomino}, which rapidly dies.URMA universal register machine, particularly Paul Chapman's Life implementation of such a machine. See {universal computer} for more information.vacuum:Empty space. That is, space containing only dead {cell}s.Venetian blindsThe p2 {agar} obtained by using the pattern O..O to tile the plane. Period 2 stabilizations of finite patches of this agar are known.&')*, "#')+, "%) $%&)!')*!#$' !$%&)* !#$()+-.%*+-.     # % ' ( +            ! " $ % ( ) * - .              ! " # $ % ' ( , - / 1 2 5 6      ) . / 1 2 6 9         ' ) + , / 6 8 :     !"#$%&(),-.12568;   !"#$%&'()+,01389;   -2356:;=>  +-/03578<>    !"#$%&'()*,-012579:<   !"#$%&'()*+,-/04567:< 19<=   /1349;>    !"#$%&'()*+,-.0145678;=     !"#$%&'()*+,-./0134589:< 58:  358:<     !"#$%&'()*+,-./012457;<      !"#$%&'()*+,-./012345      !"#$%&'()*+,-./012345     !"#$%&'()*+,-./012457;<   3 5 8 : < !! !5!8!:!"""" " " " """"""""""""""""""" "!"""#"$"%"&"'"(")"*"+","-"."/"0"1"3"4"5"8"9":"<"##### # # ################## #!#"###$#%#&#'#(#)#*#+#,#-#.#0#1#4#5#6#7#8#;#=#$$$ $ $ $$/$1$3$4$9$;$>$%%% %1%9%<%=%&&&& & &&&&&&&&&&&&&&&&&& &!&"&#&$&%&&&'&(&)&*&+&,&-&/&0&4&5&6&7&:&<&'''' ' ' '''''''''''''''' '!'"'#'$'%'&'''(')'*','-'0'1'2'5'7'9':'<'(((( ( (((((+(-(/(0(3(5(7(8(<(>())))) ) ) ))-)2)3)5)6):);)=)>)*** * *************** *!*"*#*$*%*&*'*(*)*+*,*0*1*3*8*9*;*+++ + + ++++++++++++++ +!+"+#+$+%+&+(+)+,+-+.+1+2+5+6+8+;+,,,,,,,,',),+,,,/,6,8,:,-- - ----)-.-/-1-2-6-9-. . . ............. .!.".#.$.%.'.(.,.-./.1.2.5.6./////////// /!/"/$/%/(/)/*/-/./00000#0%0'0(0+011111%1*1+1-1.12222222222 2!2#2$2(2)2+2-2.23333333 3!3$3%3&3)3*34444!4#4$4'455555!5'5)5*566666 6$6%6&6)67777 7"7%7)78888888 8"8#8'8)8+8,8999999&9'9)9*9,9?: very long = {long long}very long houseThe following {induction coil}.  volatilityiThe volatility of an {oscillator} is the size (in cells) of its {rotor} divided by the sum of the sizes of its rotor and its {stator}. In other words, it is the proportion of cells involved in the oscillator which actually oscillate. For many periods there are known oscillators with volatility 1, see for example {Achim's p16}, {figure-8}, {Kok's galaxy}, {mazing}, {pentadecathlon}, {phoenix}, {relay}, {smiley} and {tumbler}. Such an oscillator of period 3 was found in August 2012 by Jason Summers. The smallest period for which the existence of such statorless oscillators is undecided is 7. There are oscillators with volatility arbitrarily close to 1 for all but finitely many periods, because of the possibility of feeding the gliders from a {true} period n {gun} into an {eater}. The term "volatility" is due to Robert Wainwright. See also {strict volatility}.                                                volcanoAny of a number of p5 oscillators which produce sparks. See {lightweight volcano}, {middleweight volcano} and {heavyweight volcano}.von Neumann neighbourhoodOThe set of all cells that are orthogonally adjacent to a cell or group of cells. The von Neumann neighbourhood of a cell can be thought of as the points at a Manhattan distance of 1 from that cell. Compare {Moore neighbourhood}. Cell neighbourhoods can also be defined with a higher range. The von Neumann neighbourhood of range n can be defined recursively as the von Neumann neighbourhood of the von Neumann neighbourhood of range n-1. For example, the von Neumann neighbourhood of range 2 is the set of all cells that are orthogonally adjacent to the range-1 von Neumann neighbourhood. V-pentominoDConway's name for the following {pentomino}, a {loaf} {predecessor}.V sparkA common three-bit {polyplet} {spark}, produced most notably by the {pentadecathlon}. The spark can convert a {pre-block} or {block} into a {glider} as shown here: Also see {PD-pair reflector}.Wainwright's tagalongA small p4 c/4 diagonal {tagalong} that has 7 cells in every phase. It is shown here attached to the back of a {Canada goose}.+                    washerwomanPA {fuse} discovered by Earl Abbe, published in {LifeLine} Vol 3, September 1971. 2c/3 p18 fuse- $*06  #%)+/157 $*068washing machine,Found by Robert Wainwright before June 1972.p2waspThe following {spaceship} which produces a {domino} {spark} at the back. It is useful for {perturb}ing other objects. Found by David Bell, March 1998.c/3 orthogonallyp35               waterbear3c/79 obliquely, p158) A {self-supporting} oblique {macro-spaceship} constructed by Brett Berger on December 28, 2014. It is currently the fastest oblique macro-spaceship in Conway's Game of Life by several orders of magnitude, and is also the smallest known oblique macro-spaceship in terms of bounding box, superseding the {Parallel HBK}. It is no longer the smallest or fastest oblique spaceship due to the discovery in 2018 of the {elementary} {knightship} {Sir Robin}. Previous oblique spaceships, the {Gemini} and the {half-baked knightship}s, are stationary throughout almost all of their life cycles, as they construct the necessary mechanisms to support a sudden short move. The waterbear constructs support for {reburnable fuse} reactions involving {(23,5)c/79 Herschel climber}s that are in constant motion.(23,5wave)A wick-like structure attached at both ends to moving spaceship-like patterns, in such a way that the entire pattern is mobile. Especially if the wave gets longer over time, the supporting patterns are {wavestretcher}s. Also, the gliders or spaceships emitted by a rake may be referred to as a wave, again because the line as a whole appears to move in a different direction from the individual components, due to the rake's movement. Compare with {stream}. In general a wave can be interpreted as moving at a variety of different velocities, depending on which specific subcomponents are chosen as the starting and ending points for calculating speed and direction. See {antstretcher}, {wavestretcher} for a practical example of identical wave ends being connected to spaceships with different velocities. wavefront*Found by Dave Buckingham, 1976 or earlier.p4$                      waveguide= {superstring}. wavestretcherA {spaceship} pattern that supports a connection to an extensible periodic {wick}-like structure, whose speed and/or direction of propagation are different from those of the wavestretcher spaceship. Connecting the following to a standard diagonal {antstretcher} creates a new oblique {wavestretcher} (a type of {growing spaceship}) and also an alternate {space nonfiller} mechanism. A required supporting c/5 {spark} is shown at the right edge. It can be supplied by a {spider} or another c/5 orthogonal spaceship with a similar {edge spark}. Alternatively, the c/5 component could theoretically be replaced by a supporting spaceship travelling diagonally at c/6, to support the same oblique trail of ants. As of June 2018 no workable c/6 component has been found.778584125031-12,./+ , / + , . / + . 1 2 * + 2 3 + - . 0 2 3 *,-.0*,.0(,'(%&'*"#%&#$&##&"%"#$% "#%% !$# !!! !5!6!7!""""""!"8"<"###### #5#9#$$$$ $ $$$/$0$2$6$8$9$:$;$%%%% % %%%%%%%%#%$%'%(%*%+%,%.%3%9%<%&& & &&&&&&&&"&$&'&(&)&+&,&.&0&4&;& ' '''''''"'$'&')'*'-'0'4'5'6'7'(((((((("(%())!)&)1)2)6)7)'*2*$+$,%,=-wedgeA 26-cell quadratic growth pattern found by Nick Gotts in March 2006, based on ideas found in {metacatacryst} and {Gotts dots}. It held the record for the smallest-population quadratic growth pattern for eight years, until it was surpassed by {25-cell quadratic growth}. See {switch-engine ping-pong} for the lowest-population {superlinear growth} pattern as of July 2018, along with a list of the record-holders. wedge grow = {wedge}. weekender2Found by David Eppstein in January 2000. In April 2000 Stephen Silver found a tagalong for a pair of weekenders. At present, n weekenders pulling n-1 tagalongs constitute the only known {spaceship}s of this speed or period, except for variants of the {weekender distaff} that suppress its output gliders.2c/7 orthogonallyp7$            weekender distaffThe first orthogonal 2c/7 rake, constructed by Ivan Fomichev on May 22nd, 2014. It uses the weak {spark}s from {weekender}s to perturb an LWSS into an active reaction in a variable-period loop, which produces a series of {slow salvo} gliders that finally rebuilds the LWSS.2c/7p16982weldTo join two or more {still life}s or {oscillator}s together. This is often done in order to fit the objects into a smaller space than would otherwise be possible. The simplest useful example is probably the {integral sign}, which can be considered as a pair of welded {eater1}s./Wheels, Life, and other Mathematical AmusementsOne of Martin Gardner's books (1983) that collects together material from his column in Scientific American. The last three chapters of this book contain all the Life stuff.why not$Found by Dave Buckingham, July 1977.p2wickA stable or oscillating linearly repeating pattern that can be made to {burn} at one end. See {fuse}. Wicks are often fairly dense, with repeating units directly connected or at least adjacent to each other, as in the beehive {lightspeed wire} for example. However, sparse wicks such as the blocks in the {31c/240 Herschel-pair climber} are known, and arbitrarily sparse wicks can be constructed. wickstretcherkA {spaceship}-like object which stretches a {wick} that is fixed at the other end. The wick here is assumed to be in some sense connected, otherwise most {puffer}s would qualify as wickstretchers. The first example of a wickstretcher was found in October 1992 (front end by Hartmut Holzwart and back end by Dean Hickerson) and stretches {ants} at a speed of c/4. This is shown below with an improved back end found by Hickerson the following month. Diagonally moving c/4 and c/12 wickstretchers have also been built: see {tubstretcher} and {linestretcher}. In July 2000 Jason Summers constructed a c/2 wickstretcher, stretching a p50 {traffic jam} wick, based on an earlier (October 1994) pattern by Hickerson. A c/5 diagonal wickstretcher was found in January 2011 by Matthias Merzenich, who also discovered a c/5 orthogonal wickstretcher two years later in March 2013.    $%  !#&()+   !#%&(*+#&(,-!$&()*. !#%),-/     # $ ) * /      % & ( * , - / 0        # ' ( * - /            $ % * - /    % ' ( ) . %'&1 wicktrailerAny {extensible} {tagalong} or {component} that can be attached to itself, as well as to the back of a {spaceship}. The number of generations that it takes for the component to occur again in the same place is often called the period of the wicktrailer. This has little relation to the period of the component. See {branching spaceship} for an example of a wicktrailer that is part of a p2 spaceship, but repeats itself in the same location at period 20.windmill'Found by Dean Hickerson, November 1989.p48                              wingThe following {induction coil}. This is generation 2 of {block and glider}. In an unrelated use, "wing" may also refer to an {arm} of a spaceship. WinLifeSearch{Jason Summers' GUI version of {lifesrc} for MS Windows. It is available from {http://entropymine.com/jason/life/software/}. Winning WaysA two-volume book (1982) by Elwyn Berlekamp, John Conway and Richard Guy on mathematical games. The last chapter of the second volume concerns Life, and outlines a proof of the existence of a {universal constructor}.wire`A repeating stable structure, usually fairly dense, that a {signal} can travel along without making any permanent change. Known wires include the diagonal {2c/3 wire}, and orthogonal {lightspeed wire} made from a chain of beehives. Diagonal lightspeed wires are known, but the required signals are fairly complex and have no known {glider synthesis}.with the grainA term used for {negative spaceship}s travelling in {zebra stripes} agar, parallel to the stripes, and also for {with-the-grain grey ship}s. Below are three small examples of "negative spaceships" found by Gabriel Nivasch in July 1999, travelling with the grain through a stabilized finite segment of zebra stripes agar: It has been proven that signals travelling non-destructively with the grain through zebra stripes cannot travel at less than the {speed of light}. "%(+.14      !"#$%&'()*+,-./01234      !"#$%&'()*+,-./012345      !"#$%&'()*+,-./012340      !"#$%&'(*+,-234*+15                          ! " # $ % & , - . / 0 1 2 3 4 -                           ! " # $ . / 2 3 4 & ( . / 1 5                           ! " # $ ( . / 0 2 3 4 -      !"#$%&,-./01234*+15      !"#$%&'(*+,-2340      !"#$%&'()*+,-./012345      !"#$%&'()*+,-./01234     !"#&'(+,-./01234 !%&*+.5      %*01234 !%&*+/     !"#&'(+,-./012345      !"#$%&'()*+,-./01234      !"#$%&'()*+,-./01234 5 !!!!!!!! ! ! ! ! !!!!!!!!!!!!!!!!!!! !!!"!#!$!%!&!'!(!)!*!+!,!-!.!/!0!1!2!3!4!######## # # # # ############### #!#$#%#&#)#*#+#.#/#0#1#2#3#4#$$$$$#$$$($)$-$.$5$%%%%%%%% % % % % %%%%%%%%%%%%% %!%%%&%*%+%/%0%1%2%3%4%0&'''''''' ' ' ' ' '''''''''1'2'3'4'(1(5()))))))) ) ) ) ) )))))))))1)2)3)4)0*++++++++ + + + + +++++++++++++ +!+%+&+*+++/+0+1+2+3+4+,,,,,#,$,(,),-,.,5,-------- - - - - --------------- -!-$-%-&-)-*-+-.-/-0-1-2-3-4-//////// / / / / /////////////////// /!/"/#/$/%/&/'/(/)/*/+/,/-/.///0/1/2/3/4/05011111111 1 1 1 1 1111111111111111111 1!1"1#1$1%1&1'1(1)1*1+1,1-1.1/1011121314133333333 3 3 3 3 3333333333333333333 3!3"3#3$3%3&3'3(3)3*3+3,3-3.3/30313233343444 4 4444444"4%4(4+4.4144465with-the-grain grey shipA {grey ship} in which the region of density 1/2 consists of lines of ON cells lying parallel to the direction in which the spaceship moves. See also {against-the-grain grey ship}.WLS= {WinLifeSearch} worker beeoFound by Dave Buckingham in 1972. Unlike the similar {snacker} this produces no {spark}s, and so is not very important. Like the snacker, the worker bee is {extensible}. It is, in fact, a finite version of the infinite oscillator which consists of six ON cells and two OFF cells alternating along a line. Note that Dean Hickerson's new snacker ends also work here.p9"              W-pentominoKConway's name for the following {pentomino}, a common {loaf} {predecessor}.*WSSAny of the standard orthogonal {spaceship}s - {LWSS}, {MWSS}, or {HWSS}. At one point the term {fish} was more common for this group of spaceships.x66-Found by Hartmut Holzwart, July 1992. Half of this can be escorted by an HWSS. The name refers to the fact that every cell (live or dead) has at most 6 live neighbours (in contrast to {spaceship}s based on {LWSS}, {MWSS} or {HWSS}). In fact this spaceship was found by a search with this restriction.c/2 orthogonallyp4"   XlifeA popular freeware Life program that runs under the X Window System. The main Life code was written by Jon Bennett, and the X code by Chuck Silvers. X-pentominoMConway's name for the following {pentomino}, a {traffic light} {predecessor}. Y-pentomino@Conway's name for the following {pentomino}, which rapidly dies. zebra stripes`A stable agar consisting of alternating bands of live and dead cells. Known {spacefiller}s and many {gray ship}s create patches of this agar. It is also the medium through which {with the grain} and {against the grain} {negative spaceship}s travel. Many simple stabilizations of the boundaries of finite regions of this agar are known, as shown below.p1                                                                                          Z-hexomino`The following {hexomino}. The Z-hexomino features in the {pentoad}, and also in {Achim's p144}.zone of influence&The set of cells on which a chosen cell or pattern can potentially exert an influence in a given number of generations N. If N is not specified it is generally taken to be one, in which case the zone of influence simply coincides with the Moore neighbourhood of the cell or pattern. The set for N generations consists of all the cells to which at least N paths of length N can be traced from the cell(s) in question. Contrast this with the range-N Moore neighbourhood, which consists of all cells to which at least one path of length n can be traced. Z-pentomino@Conway's name for the following {pentomino}, which rapidly dies.zweibackAn oscillator in which two {HW volcano}es {hassle} a {loaf}. This was found by Mark Niemiec in February 1995. A smaller version using Scot Ellison's reduced HW volcano is shown below.p30          !   ! !"#%  $%  !"  !#$%&'         ! (    ! " # $ ' (            " #      " #       !"#$'(  !(  !#$%&' !"   $%   !"#% !    !  )