YES
O(n^2)
TRS:
 {
     a__f(X1, X2, X3) -> f(X1, X2, X3),
      a__f(a(), X, X) -> a__f(X, a__b(), b()),
               a__b() -> b(),
               a__b() -> a(),
            mark(b()) -> a__b(),
            mark(a()) -> a(),
  mark(f(X1, X2, X3)) -> a__f(X1, mark(X2), X3)
 }
 DUP: We consider a non-duplicating system.
  Trs:
   {
       a__f(X1, X2, X3) -> f(X1, X2, X3),
        a__f(a(), X, X) -> a__f(X, a__b(), b()),
                 a__b() -> b(),
                 a__b() -> a(),
              mark(b()) -> a__b(),
              mark(a()) -> a(),
    mark(f(X1, X2, X3)) -> a__f(X1, mark(X2), X3)
   }
  Matrix Interpretation:
   Interpretation class: triangular
       [X5]  [X3]  [X1]    [1 2][X5]   [1 0][X3]   [1 2][X1]   [0]
   [f]([X4], [X2], [X0]) = [0 1][X4] + [0 1][X2] + [0 1][X0] + [2]
   
          [X1]    [1 2][X1]   [2]
   [mark]([X0]) = [0 1][X0] + [3]
   
         [0]
   [a] = [3]
   
         [0]
   [b] = [0]
   
            [1]
   [a__b] = [3]
   
          [X5]  [X3]  [X1]    [1 3][X5]   [1 0][X3]   [1 3][X1]   [1]
   [a__f]([X4], [X2], [X0]) = [0 1][X4] + [0 1][X2] + [0 1][X0] + [2]
   
   
   Qed