TRS: {plus(s(s(x)), y) -> s(plus(x, s(y))), plus(x, s(s(y))) -> s(plus(s(x), y)), plus(s(0()), y) -> s(y), plus(0(), y) -> y, ack(0(), y) -> s(y), ack(s(x), 0()) -> ack(x, s(0())), ack(s(x), s(y)) -> ack(x, plus(y, ack(s(x), y)))} Fail