YES(O(1),O(n^2)) We are left with following problem, upon which TcT provides the certificate YES(O(1),O(n^2)). Strict Trs: { sum(0()) -> 0() , sum(s(x)) -> +(sum(x), s(x)) , +(x, 0()) -> x , +(x, s(y)) -> s(+(x, y)) } Obligation: innermost runtime complexity Answer: YES(O(1),O(n^2)) We use the processor 'Small Polynomial Path Order (PS,2-bounded)' to orient following rules strictly. Trs: { sum(0()) -> 0() , sum(s(x)) -> +(sum(x), s(x)) , +(x, 0()) -> x , +(x, s(y)) -> s(+(x, y)) } The induced complexity on above rules (modulo remaining rules) is YES(?,O(n^2)) . These rules are moved into the corresponding weak component(s). Sub-proof: ---------- The input was oriented with the instance of 'Small Polynomial Path Order (PS,2-bounded)' as induced by the safe mapping safe(sum) = {}, safe(0) = {}, safe(s) = {1}, safe(+) = {1} and precedence sum > + . Following symbols are considered recursive: {sum, +} The recursion depth is 2. For your convenience, here are the satisfied ordering constraints: sum(0();) > 0() sum(s(; x);) > +(s(; x); sum(x;)) +(0(); x) > x +(s(; y); x) > s(; +(y; x)) We return to the main proof. We are left with following problem, upon which TcT provides the certificate YES(O(1),O(1)). Weak Trs: { sum(0()) -> 0() , sum(s(x)) -> +(sum(x), s(x)) , +(x, 0()) -> x , +(x, s(y)) -> s(+(x, y)) } Obligation: innermost runtime complexity Answer: YES(O(1),O(1)) Empty rules are trivially bounded Hurray, we answered YES(O(1),O(n^2))