alias-index := (: LEOF List<Tuple<Tuple<String,String>,Type>>);

add-alias := λ(: from String)(: to String)(: tt Type). (: (
   (set alias-index (cons( (Tuple( (Tuple( from to )) tt )) alias-index )))
) Nil);

find-alias := λ(: from String)(: pars Type). (: (
   (let to from)
   (for-each (alias in alias-index) (
      (match alias (
         ()
         ( (Tuple(
              (Tuple( alt-from alt-to ))
              (TGround( 'Arrow_s (LCons( _ (LCons( alt-domain LEOF )) )) ))
           )) (
            (if (&&( (==( from alt-from )) (can-unify( alt-domain pars )) )) (
               (set to alt-to)
            ) ())
         ))
      ))
   ))
   to
) String);

find-alias-type := λ(: from String). (: (
   (let to TAny)
   (for-each (alias in alias-index) (
      (match alias (
         ()
         ( (Tuple( (Tuple( alt-from alt-to )) alt-tt )) (
            (if (==( from alt-from )) (
               (if (non-zero to) (
                  (set to (and( to alt-tt )))
               ) (
                  (set to alt-tt)
               ))
            ) ())
         ))
      ))
   ))
   to
) Type);