app app app if true x y x app app app if false x y y app app filter f nil nil app app filter f app app cons x xs app app app if app f x app app cons x app app filter f xs app app filter f xs app 2 if 0 true 0 false 0 filter 0 nil 0 cons 0 FULL ./TRS/higher-order/AotoYam/015.trs