YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { a__f(X) -> f(X) , a__f(0()) -> cons(0(), f(s(0()))) , a__f(s(0())) -> a__f(a__p(s(0()))) , a__p(X) -> p(X) , a__p(s(0())) -> 0() , mark(0()) -> 0() , mark(cons(X1, X2)) -> cons(mark(X1), X2) , mark(f(X)) -> a__f(mark(X)) , mark(s(X)) -> s(mark(X)) , mark(p(X)) -> a__p(mark(X)) } Obligation: innermost runtime complexity Answer: YES(?,O(n^1)) The problem is match-bounded by 3. The enriched problem is compatible with the following automaton. { a__f_0(2) -> 1 , a__f_1(7) -> 1 , a__f_1(8) -> 1 , a__f_1(8) -> 8 , a__f_2(11) -> 1 , a__f_2(11) -> 8 , 0_0() -> 2 , 0_1() -> 1 , 0_1() -> 3 , 0_1() -> 6 , 0_1() -> 8 , 0_2() -> 1 , 0_2() -> 7 , 0_2() -> 8 , 0_3() -> 11 , cons_0(2, 2) -> 2 , cons_1(3, 4) -> 1 , cons_1(8, 2) -> 1 , cons_1(8, 2) -> 8 , cons_2(7, 9) -> 1 , cons_2(7, 9) -> 8 , cons_3(11, 12) -> 1 , cons_3(11, 12) -> 8 , f_0(2) -> 2 , f_1(2) -> 1 , f_1(5) -> 4 , f_2(7) -> 1 , f_2(8) -> 1 , f_2(8) -> 8 , f_2(10) -> 9 , f_3(11) -> 1 , f_3(11) -> 8 , f_3(13) -> 12 , s_0(2) -> 2 , s_1(6) -> 5 , s_1(8) -> 1 , s_1(8) -> 8 , s_2(7) -> 10 , s_3(11) -> 13 , a__p_0(2) -> 1 , a__p_1(5) -> 7 , a__p_1(8) -> 1 , a__p_1(8) -> 8 , a__p_2(10) -> 11 , mark_0(2) -> 1 , mark_1(2) -> 8 , p_0(2) -> 2 , p_1(2) -> 1 , p_2(5) -> 7 , p_2(8) -> 1 , p_2(8) -> 8 , p_3(10) -> 11 } Hurray, we answered YES(?,O(n^1))