YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { add(0(), x) -> x , add(s(x), y) -> s(add(x, y)) } Obligation: innermost runtime complexity Answer: YES(?,O(n^1)) The input was oriented with the instance of 'Small Polynomial Path Order (PS)' as induced by the safe mapping safe(add) = {}, 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(?,O(n^1))