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