YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { add0(x', Cons(x, xs)) -> add0(Cons(Cons(Nil(), Nil()), x'), xs) , add0(x, Nil()) -> x , notEmpty(Cons(x, xs)) -> True() , notEmpty(Nil()) -> False() , goal(x, y) -> add0(x, 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(add0) = {1}, safe(Cons) = {1, 2}, safe(Nil) = {}, safe(notEmpty) = {}, safe(True) = {}, safe(False) = {}, safe(goal) = {1} and precedence notEmpty > add0, goal > add0, notEmpty ~ goal . Following symbols are considered recursive: {add0} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: add0(Cons(; x, xs); x') > add0(xs; Cons(; Cons(; Nil(), Nil()), x')) add0(Nil(); x) > x notEmpty(Cons(; x, xs);) > True() notEmpty(Nil();) > False() goal(y; x) > add0(y; x) Hurray, we answered YES(?,O(n^1))