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