TRS: { -(x, 0()) -> x, -(s(x), s(y)) -> -(x, y), <=(0(), y) -> true(), <=(s(x), 0()) -> false(), <=(s(x), s(y)) -> <=(x, y), if(true(), x, y) -> x, if(false(), x, y) -> y, perfectp(0()) -> false(), perfectp(s(x)) -> f(x, s(0()), s(x), s(x)), f(0(), y, 0(), u) -> true(), f(0(), y, s(z), u) -> false(), f(s(x), 0(), z, u) -> f(x, u, -(z, s(x)), u), f(s(x), s(y), z, u) -> if(<=(x, y), f(s(x), -(y, x), z, u), f(x, u, z, u))} Fail