We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { f(g(x)) -> g(g(f(x))) , f(g(x)) -> g(g(g(x))) } Obligation: runtime complexity Answer: YES(?,O(n^1)) The input is overlay and right-linear. Switching to innermost rewriting. We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { f(g(x)) -> g(g(f(x))) , f(g(x)) -> g(g(g(x))) } 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(f) = {}, safe(g) = {1} and precedence empty . Following symbols are considered recursive: {f} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: f(g(; x);) > g(; g(; f(x;))) f(g(; x);) > g(; g(; g(; x))) Hurray, we answered YES(?,O(n^1))