TRS: { 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, minus(z, s(x)), u), f(s(x), s(y), z, u) -> if(le(x, y), f(s(x), minus(y, x), z, u), f(x, u, z, u))} Fail