YES(?,POLY) We are left with following problem, upon which TcT provides the certificate YES(?,POLY). Strict Trs: { add(0(), x) -> x , add(s(x), y) -> s(add(x, y)) } 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(add) = {2}, safe(0) = {}, safe(s) = {1} and precedence empty . Following symbols are considered recursive: {add} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: add(0(); x) > x add(s(; x); y) > s(; add(x; y)) Hurray, we answered YES(?,POLY)