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