YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { f(nil()) -> nil() , f(.(nil(), y)) -> .(nil(), f(y)) , f(.(.(x, y), z)) -> f(.(x, .(y, z))) , g(nil()) -> nil() , g(.(x, nil())) -> .(g(x), nil()) , g(.(x, .(y, z))) -> g(.(.(x, y), z)) } Obligation: innermost runtime complexity Answer: YES(?,O(n^1)) The problem is match-bounded by 1. The enriched problem is compatible with the following automaton. { f_0(2) -> 1 , f_0(3) -> 1 , f_1(2) -> 5 , f_1(3) -> 5 , f_1(6) -> 1 , f_1(6) -> 5 , f_1(7) -> 5 , nil_0() -> 2 , nil_1() -> 1 , nil_1() -> 4 , nil_1() -> 5 , nil_1() -> 8 , ._0(2, 2) -> 3 , ._0(2, 3) -> 3 , ._0(3, 2) -> 3 , ._0(3, 3) -> 3 , ._1(1, 5) -> 1 , ._1(2, 2) -> 7 , ._1(2, 3) -> 7 , ._1(2, 6) -> 6 , ._1(2, 7) -> 6 , ._1(3, 2) -> 7 , ._1(3, 3) -> 7 , ._1(3, 6) -> 6 , ._1(3, 7) -> 6 , ._1(5, 5) -> 5 , ._1(7, 2) -> 9 , ._1(7, 3) -> 9 , ._1(8, 4) -> 4 , ._1(8, 8) -> 8 , ._1(9, 2) -> 9 , ._1(9, 3) -> 9 , g_0(2) -> 4 , g_0(3) -> 4 , g_1(2) -> 8 , g_1(3) -> 8 , g_1(7) -> 8 , g_1(9) -> 4 , g_1(9) -> 8 } Hurray, we answered YES(?,O(n^1))