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