YES
O(n^2)
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())}
  Matrix Interpretation:
   Interpretation class: triangular
       [X1]    [1 0][X1]   [0]
   [g]([X0]) = [0 0][X0] + [0]
   
         [0]
   [a] = [2]
   
         [2]
   [b] = [0]
   
       [X1]    [1 2][X1]   [2]
   [f]([X0]) = [0 1][X0] + [1]
   
   
   Qed