MAYBE
MAYBE
TRS:
 {
     ack(s(x), y) -> f(x, x),
  ack(s(x), s(y)) -> ack(x, ack(s(x), y)),
   ack(s(x), 0()) -> ack(x, s(0())),
      ack(0(), y) -> s(y),
          f(x, y) -> ack(x, y),
       f(x, s(y)) -> f(y, x),
       f(s(x), y) -> f(x, s(x))
 }
 DUP: We consider a duplicating system.
  Trs:
   {
       ack(s(x), y) -> f(x, x),
    ack(s(x), s(y)) -> ack(x, ack(s(x), y)),
     ack(s(x), 0()) -> ack(x, s(0())),
        ack(0(), y) -> s(y),
            f(x, y) -> ack(x, y),
         f(x, s(y)) -> f(y, x),
         f(s(x), y) -> f(x, s(x))
   }
  Fail