YES(?,O(n^2))
TRS:
 {f(a(), f(f(a(), x), a())) -> f(f(a(), f(a(), x)), a())}
 DUP: We consider a non-duplicating system.
  Trs:
   {f(a(), f(f(a(), x), a())) -> f(f(a(), f(a(), x)), a())}
  Matrix Interpretation:
   Interpretation class: triangular
         [0]
   [a] = [0]
   
       [X3]  [X1]    [1 1][X3]   [1 3][X1]   [0]
   [f]([X2], [X0]) = [0 1][X2] + [0 1][X0] + [3]
   
   
   Qed