YES
O(n^4)
TRS:
 {f(f(a(), f(x, a())), a()) -> f(a(), f(f(x, a()), a()))}
 DUP: We consider a non-duplicating system.
  Trs:
   {f(f(a(), f(x, a())), a()) -> f(a(), f(f(x, a()), a()))}
  Matrix Interpretation:
   Interpretation class: triangular
         [0]
         [0]
   [a] = [0]
         [0]
   
       [X7]  [X3]    [1 0 1 0][X7]   [1 0 0 0][X3]   [0]
       [X6]  [X2]    [0 0 0 1][X6]   [0 0 1 0][X2]   [0]
   [f]([X5], [X1]) = [0 0 0 1][X5] + [0 0 0 1][X1] + [0]
       [X4]  [X0]    [0 0 0 1][X4]   [0 0 0 1][X0]   [1]
   
   
   Qed