MAYBE
Trs:
 {               f(x, nil()) -> g(nil(), x),
               f(x, g(y, z)) -> g(f(x, y), z),
                ++(x, nil()) -> x,
              ++(x, g(y, z)) -> g(++(x, y), z),
               mem(nil(), y) -> false(),
             mem(g(x, y), z) -> or(=(y, z), mem(x, z)),
              mem(x, max(x)) -> not(null(x)),
                 null(nil()) -> true(),
               null(g(x, y)) -> false(),
      max(g(g(nil(), x), y)) -> max'(x, y),
  max(g(g(g(x, y), z), u())) -> max'(max(g(g(x, y), z)), u())}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open