app app map f nil nil app app map f app app cons x xs app app cons app f x app app map f xs app flatten app app node x xs app app cons x app concat app app map flatten xs app concat nil nil app concat app app cons x xs app app append x app concat xs app app append nil xs xs app app append app app cons x xs ys app app cons x app app append xs ys app 2 map 0 nil 0 cons 0 flatten 0 node 0 concat 0 append 0 FULL ./TRS/higher-order/Bird/TreeFlatten.trs