: merge ( x y z -- z )
[| a b c | a b c a length 0 > b length 0 > and ]
[| a b c | a b c 0 a nth 0 b nth over over < 
  [| a b c x y | 0 a remove-nth b x c push ]
  [| a b c x y | a 0 b remove-nth y c push ]
  if
] while
[| x y z | x y z y 0 = [| x y z | x z append ] [| x y z | y z append ] if ] call
;