YES(?,PRIMREC) We are left with following problem, upon which TcT provides the certificate YES(?,PRIMREC). 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(?,PRIMREC) The input was oriented with the instance of'multiset path order' as induced by the precedence sum > s, sum > +, 0 > s, 0 > +, s > +, sum1 > s, sum1 > +, sum ~ 0, sum ~ sum1, 0 ~ sum1 . Hurray, we answered YES(?,PRIMREC)