TRS:
 {                 concat(leaf(), Y) -> Y,
               concat(cons(U, V), Y) -> cons(U, concat(V, Y)),
               lessleaves(X, leaf()) -> false(),
      lessleaves(leaf(), cons(W, Z)) -> true(),
  lessleaves(cons(U, V), cons(W, Z)) -> lessleaves(concat(U, V), concat(W, Z))}
 Fail