YES
O(n)
TRS:
 {f(a()) -> g(a()),
     b() -> a(),
  g(b()) -> f(b())}
 DUP: We consider a non-duplicating system.
  Trs:
   {f(a()) -> g(a()),
       b() -> a(),
    g(b()) -> f(b())}
  BOUND:
   Automaton:
    {
       a_2() -> 15,
       a_1() -> 5,
       a_0() -> 4,
     g_2(17) -> 18,
     g_1(11) -> 12,
      g_0(4) -> 4,
       b_1() -> 7,
       b_0() -> 4,
      f_1(7) -> 8,
      f_0(4) -> 4,
          18 -> 8,
          15 -> 17 | 7,
          12 -> 4,
           8 -> 4,
           5 -> 11 | 4
    }
   Strict:
    {}
   Qed