YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { f(X) -> n__f(X) , f(0()) -> cons(0(), n__f(n__s(n__0()))) , f(s(0())) -> f(p(s(0()))) , 0() -> n__0() , s(X) -> n__s(X) , p(s(X)) -> X , activate(X) -> X , activate(n__f(X)) -> f(activate(X)) , activate(n__s(X)) -> s(activate(X)) , activate(n__0()) -> 0() } Obligation: runtime complexity Answer: YES(?,O(n^1)) The problem is match-bounded by 4. The enriched problem is compatible with the following automaton. { f_0(2) -> 1 , f_1(3) -> 1 , f_1(3) -> 3 , f_2(8) -> 1 , f_2(8) -> 3 , 0_0() -> 1 , 0_1() -> 1 , 0_1() -> 3 , 0_2() -> 4 , 0_2() -> 8 , 0_3() -> 10 , cons_0(2, 2) -> 1 , cons_0(2, 2) -> 2 , cons_0(2, 2) -> 3 , cons_2(4, 5) -> 1 , cons_2(8, 5) -> 3 , cons_3(10, 11) -> 1 , cons_3(10, 11) -> 3 , n__f_0(2) -> 1 , n__f_0(2) -> 2 , n__f_0(2) -> 3 , n__f_1(2) -> 1 , n__f_2(3) -> 1 , n__f_2(3) -> 3 , n__f_2(6) -> 5 , n__f_3(8) -> 1 , n__f_3(8) -> 3 , n__f_3(9) -> 11 , n__s_0(2) -> 1 , n__s_0(2) -> 2 , n__s_0(2) -> 3 , n__s_1(2) -> 1 , n__s_2(3) -> 1 , n__s_2(3) -> 3 , n__s_2(7) -> 6 , n__s_3(4) -> 9 , n__0_0() -> 1 , n__0_0() -> 2 , n__0_0() -> 3 , n__0_1() -> 1 , n__0_2() -> 1 , n__0_2() -> 3 , n__0_2() -> 7 , n__0_3() -> 4 , n__0_3() -> 8 , n__0_4() -> 10 , s_0(2) -> 1 , s_1(3) -> 1 , s_1(3) -> 3 , s_2(4) -> 9 , p_0(2) -> 1 , p_2(9) -> 8 , activate_0(2) -> 1 , activate_1(2) -> 3 , 2 -> 1 , 2 -> 3 , 4 -> 8 } Hurray, we answered YES(?,O(n^1))