We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { active(f(X)) -> f(active(X)) , active(f(0())) -> mark(cons(0(), f(s(0())))) , active(f(s(0()))) -> mark(f(p(s(0())))) , active(cons(X1, X2)) -> cons(active(X1), X2) , active(s(X)) -> s(active(X)) , active(p(X)) -> p(active(X)) , active(p(s(X))) -> mark(X) , f(mark(X)) -> mark(f(X)) , f(ok(X)) -> ok(f(X)) , cons(mark(X1), X2) -> mark(cons(X1, X2)) , cons(ok(X1), ok(X2)) -> ok(cons(X1, X2)) , s(mark(X)) -> mark(s(X)) , s(ok(X)) -> ok(s(X)) , p(mark(X)) -> mark(p(X)) , p(ok(X)) -> ok(p(X)) , proper(f(X)) -> f(proper(X)) , proper(0()) -> ok(0()) , proper(cons(X1, X2)) -> cons(proper(X1), proper(X2)) , proper(s(X)) -> s(proper(X)) , proper(p(X)) -> p(proper(X)) , top(mark(X)) -> top(proper(X)) , top(ok(X)) -> top(active(X)) } Obligation: runtime complexity Answer: YES(?,O(n^1)) The problem is match-bounded by 2. The enriched problem is compatible with the following automaton. { active_0(3) -> 1 , active_0(4) -> 1 , active_0(9) -> 1 , active_1(3) -> 16 , active_1(4) -> 16 , active_1(9) -> 16 , active_2(15) -> 17 , f_0(3) -> 2 , f_0(4) -> 2 , f_0(9) -> 2 , f_1(3) -> 11 , f_1(4) -> 11 , f_1(9) -> 11 , 0_0() -> 3 , 0_1() -> 15 , mark_0(3) -> 4 , mark_0(4) -> 4 , mark_0(9) -> 4 , mark_1(11) -> 2 , mark_1(11) -> 11 , mark_1(12) -> 5 , mark_1(12) -> 12 , mark_1(13) -> 6 , mark_1(13) -> 13 , mark_1(14) -> 7 , mark_1(14) -> 14 , cons_0(3, 3) -> 5 , cons_0(3, 4) -> 5 , cons_0(3, 9) -> 5 , cons_0(4, 3) -> 5 , cons_0(4, 4) -> 5 , cons_0(4, 9) -> 5 , cons_0(9, 3) -> 5 , cons_0(9, 4) -> 5 , cons_0(9, 9) -> 5 , cons_1(3, 3) -> 12 , cons_1(3, 4) -> 12 , cons_1(3, 9) -> 12 , cons_1(4, 3) -> 12 , cons_1(4, 4) -> 12 , cons_1(4, 9) -> 12 , cons_1(9, 3) -> 12 , cons_1(9, 4) -> 12 , cons_1(9, 9) -> 12 , s_0(3) -> 6 , s_0(4) -> 6 , s_0(9) -> 6 , s_1(3) -> 13 , s_1(4) -> 13 , s_1(9) -> 13 , p_0(3) -> 7 , p_0(4) -> 7 , p_0(9) -> 7 , p_1(3) -> 14 , p_1(4) -> 14 , p_1(9) -> 14 , proper_0(3) -> 8 , proper_0(4) -> 8 , proper_0(9) -> 8 , proper_1(3) -> 16 , proper_1(4) -> 16 , proper_1(9) -> 16 , ok_0(3) -> 9 , ok_0(4) -> 9 , ok_0(9) -> 9 , ok_1(11) -> 2 , ok_1(11) -> 11 , ok_1(12) -> 5 , ok_1(12) -> 12 , ok_1(13) -> 6 , ok_1(13) -> 13 , ok_1(14) -> 7 , ok_1(14) -> 14 , ok_1(15) -> 8 , ok_1(15) -> 16 , top_0(3) -> 10 , top_0(4) -> 10 , top_0(9) -> 10 , top_1(16) -> 10 , top_2(17) -> 10 } Hurray, we answered YES(?,O(n^1))