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))