app nil l l app cons n l y cons n app l y reverse nil nil reverse cons n l app reverse l cons n nil shuffle nil nil shuffle cons n l cons n shuffle reverse l uhalf 0 0 uhalf s 0 s 0 uhalf s s n s uhalf n hrepeat 0 F l l hrepeat s n F l hrepeat uhalf n F F l tail cons n l l head cons n l n hshuffle l hrepeat head l z list shuffle z tail l n nat x list y list l list F list list nil list app list list list cons nat list list shuffle list list hshuffle list list reverse list list hrepeat nat list list list list 0 nat s nat nat uhalf nat nat tail list list head list nat FULL .