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