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