app nil xs xs app cons x xs ys cons x app xs ys foldl F xs nil xs foldl F xs cons y ys foldl F F xs y ys iconsc xs list x nat cons x xs reverse xs foldl iconsc nil xs reverse1 xs foldl lx list x nat app cons x nil lx nil xs x nat y nat F list nat list xs list ys list app list list list nil list cons nat list list foldl list nat list list list list reverse list list reverse1 list list iconsc list nat list FULL .