[" " split] [words]   def
[" " join]  [unwords] def

["\n" split] [lines]   def
["\n" join]  [unlines] def

["" split [pop drop rev] 2 times] [chars] def

[[s] -> s upcase s eq?]   [upcase?]   def
[[s] -> s downcase s eq?] [downcase?] def