YES
O(n)
TRS:
 {f(a()) -> f(b()),
  g(b()) -> g(a())}
 DUP: We consider a non-duplicating system.
  Trs:
   {f(a()) -> f(b()),
    g(b()) -> g(a())}
  BOUND:
   Automaton:
    {
     g_1(9) -> 10,
     g_0(4) -> 4,
      a_1() -> 9,
      a_0() -> 4,
      b_1() -> 5,
      b_0() -> 4,
     f_1(5) -> 6,
     f_0(4) -> 4,
         10 -> 4,
          6 -> 4
    }
   Strict:
    {}
   Qed