YES(?,POLY) We are left with following problem, upon which TcT provides the certificate YES(?,POLY). Strict Trs: { sum(0()) -> 0() , sum(s(x)) -> +(sum(x), s(x)) , sum1(0()) -> 0() , sum1(s(x)) -> s(+(sum1(x), +(x, x))) } Obligation: innermost runtime complexity Answer: YES(?,POLY) The input was oriented with the instance of 'Polynomial Path Order' as induced by the safe mapping safe(sum) = {}, safe(0) = {}, safe(s) = {1}, safe(+) = {1, 2}, safe(sum1) = {} and precedence sum ~ sum1 . Following symbols are considered recursive: {sum, sum1} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: sum(0();) > 0() sum(s(; x);) > +(; sum(x;), s(; x)) sum1(0();) > 0() sum1(s(; x);) > s(; +(; sum1(x;), +(; x, x))) Hurray, we answered YES(?,POLY)