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