YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { add0(S(x), x2) -> +(S(0()), add0(x2, x)) , add0(0(), x2) -> x2 } Weak Trs: { +(x, S(0())) -> S(x) , +(S(0()), y) -> S(y) } Obligation: innermost runtime complexity Answer: YES(?,O(n^1)) The input was oriented with the instance of 'Small Polynomial Path Order (PS,1-bounded)' as induced by the safe mapping safe(+) = {1, 2}, safe(S) = {1}, safe(0) = {}, safe(add0) = {} and precedence add0 > + . Following symbols are considered recursive: {add0} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: +(; x, S(; 0())) > S(; x) +(; S(; 0()), y) > S(; y) add0(S(; x), x2;) > +(; S(; 0()), add0(x2, x;)) add0(0(), x2;) > x2 Hurray, we answered YES(?,O(n^1))