YES
O(n)
TRS:
 {  f(x) -> g(x),
  f(a()) -> f(b()),
  g(b()) -> g(a())}
 DUP: We consider a non-duplicating system.
  Trs:
   {  f(x) -> g(x),
    f(a()) -> f(b()),
    g(b()) -> g(a())}
  BOUND:
   Automaton:
    {
     g_2(16) -> 17,
      g_1(5) -> 6,
      g_0(4) -> 4,
       a_2() -> 20,
       a_1() -> 13,
       a_0() -> 4,
       b_1() -> 9,
       b_0() -> 4,
      f_1(9) -> 10,
      f_0(4) -> 4,
          20 -> 16,
          17 -> 10,
          13 -> 5,
          10 -> 4,
           9 -> 16,
           6 -> 4,
           4 -> 5
    }
   Strict:
    {}
   Qed