YES
O(n^3)
TRS:
 {   f(X, X) -> c(X),
  f(X, c(X)) -> f(s(X), X),
  f(s(X), X) -> f(X, a(X))}
 DUP: We consider a non-duplicating system.
  Trs:
   {   f(X, X) -> c(X),
    f(X, c(X)) -> f(s(X), X),
    f(s(X), X) -> f(X, a(X))}
  Matrix Interpretation:
   Interpretation class: triangular
       [X2]    [1 0 0][X2]   [0]
   [c]([X1]) = [0 1 0][X1] + [1]
       [X0]    [0 0 0][X0]   [1]
   
       [X2]    [1 0 0][X2]   [0]
   [s]([X1]) = [0 0 0][X1] + [0]
       [X0]    [0 0 0][X0]   [1]
   
       [X2]    [1 0 0][X2]   [0]
   [a]([X1]) = [0 0 0][X1] + [0]
       [X0]    [0 0 0][X0]   [0]
   
       [X5]  [X2]    [1 0 1][X5]   [1 1 1][X2]   [1]
   [f]([X4], [X1]) = [0 0 0][X4] + [0 1 0][X1] + [1]
       [X3]  [X0]    [0 0 0][X3]   [0 0 0][X0]   [1]
   
   
   Qed