MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { minus(0(), y) -> 0() , minus(s(x), 0()) -> s(x) , minus(s(x), s(y)) -> minus(x, y) , le(0(), y) -> true() , le(s(x), 0()) -> false() , le(s(x), s(y)) -> le(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, 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)) } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..