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