app app app fold f nil x x app app app fold f app app cons h t x app app app fold f t app app f x h app sum l app app app fold add l 0 app app app fold mul l 1 app prod l app 2 fold 0 nil 0 cons 0 sum 0 add 0 0 0 mul 0 1 0 prod 0 FULL ./TRS/higher-order/Lifantsev/Ex6Folding.trs