YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { comp_f_g[1](walk_1(), walk_4(x11), x7) -> walk_4[1](x11, x7) , comp_f_g[1](comp_f_g(x7, walk_4(x9)), walk_4(x5), x3) -> comp_f_g[1](x7, walk_4(x9), walk_4[1](x5, x3)) , walk_4[1](x7, x11) -> Cons(x7, x11) , rec[walk_0][1](Cons(x61, x77)) -> comp_f_g(rec[walk_0][1](x77), walk_4(x61)) , rec[walk_0][1](Nil()) -> walk_1() , main(Cons(x122, x154)) -> comp_f_g[1](rec[walk_0][1](x154), walk_4(x122), Nil()) , main(Nil()) -> Nil() } 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. { walk_1_0() -> 2 , walk_1_1() -> 1 , walk_1_1() -> 4 , walk_4_0(2) -> 2 , walk_4_1(2) -> 3 , walk_4_2(2) -> 6 , comp_f_g[1]_0(2, 2, 2) -> 1 , comp_f_g[1]_1(2, 3, 1) -> 1 , comp_f_g[1]_1(4, 3, 5) -> 1 , comp_f_g[1]_2(4, 6, 1) -> 1 , walk_4[1]_0(2, 2) -> 1 , walk_4[1]_1(2, 1) -> 1 , walk_4[1]_1(2, 2) -> 1 , walk_4[1]_2(2, 1) -> 1 , walk_4[1]_2(2, 5) -> 1 , comp_f_g_0(2, 2) -> 2 , comp_f_g_1(4, 3) -> 1 , comp_f_g_1(4, 3) -> 4 , Cons_0(2, 2) -> 2 , Cons_1(2, 2) -> 1 , Cons_2(2, 1) -> 1 , Cons_2(2, 2) -> 1 , Cons_3(2, 1) -> 1 , Cons_3(2, 5) -> 1 , Nil_0() -> 2 , Nil_1() -> 1 , Nil_1() -> 5 , rec[walk_0][1]_0(2) -> 1 , rec[walk_0][1]_1(2) -> 4 , main_0(2) -> 1 } Hurray, we answered YES(?,O(n^1))