YES(?,O(n^2))

Problem:
 app(nil(),xs) -> nil()
 app(cons(x,xs),ys) -> cons(x,app(xs,ys))

Proof:
 Complexity Transformation Processor:
  strict:
   app(nil(),xs) -> nil()
   app(cons(x,xs),ys) -> cons(x,app(xs,ys))
  weak:
   
  Matrix Interpretation Processor:
   dimension: 1
   max_matrix:
    1
    interpretation:
     [cons](x0, x1) = x0 + x1,
     
     [app](x0, x1) = x0 + x1 + 1,
     
     [nil] = 1
    orientation:
     app(nil(),xs) = xs + 2 >= 1 = nil()
     
     app(cons(x,xs),ys) = x + xs + ys + 1 >= x + xs + ys + 1 = cons(x,app(xs,ys))
    problem:
     strict:
      app(cons(x,xs),ys) -> cons(x,app(xs,ys))
     weak:
      app(nil(),xs) -> nil()
    Matrix Interpretation Processor:
     dimension: 2
     max_matrix:
      [1 1]
      [0 1]
      interpretation:
                        [1 1]          [0]
       [cons](x0, x1) = [0 1]x0 + x1 + [1],
       
                       [1 1]     [1 0]     [0]
       [app](x0, x1) = [0 1]x0 + [0 0]x1 + [1],
       
               [0]
       [nil] = [1]
      orientation:
                            [1 2]    [1 1]     [1 0]     [1]    [1 1]    [1 1]     [1 0]     [0]                     
       app(cons(x,xs),ys) = [0 1]x + [0 1]xs + [0 0]ys + [2] >= [0 1]x + [0 1]xs + [0 0]ys + [2] = cons(x,app(xs,ys))
       
                       [1 0]     [1]    [0]        
       app(nil(),xs) = [0 0]xs + [2] >= [1] = nil()
      problem:
       strict:
        
       weak:
        app(cons(x,xs),ys) -> cons(x,app(xs,ys))
        app(nil(),xs) -> nil()
      Qed