YES(?,O(n^2))

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

Proof:
 RT Transformation Processor:
  strict:
   app(nil(),xs) -> nil()
   app(cons(x,xs),ys) -> cons(x,app(xs,ys))
  weak:
   
  Matrix Interpretation Processor:
   dimension: 1
   interpretation:
    [cons](x0, x1) = x0 + x1,
    
    [app](x0, x1) = x0 + x1 + 2,
    
    [nil] = 3
   orientation:
    app(nil(),xs) = xs + 5 >= 3 = nil()
    
    app(cons(x,xs),ys) = x + xs + ys + 2 >= x + xs + ys + 2 = 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
    interpretation:
                      [1 0]     [1 1]     [1]
     [cons](x0, x1) = [0 0]x0 + [0 1]x1 + [1],
     
                     [1 4]     [1  10]     [8]
     [app](x0, x1) = [0 1]x0 + [0  0 ]x1 + [3],
     
             [0]
     [nil] = [1]
    orientation:
                          [1 0]    [1 5]     [1  10]     [13]    [1 0]    [1 5]     [1  10]     [12]                     
     app(cons(x,xs),ys) = [0 0]x + [0 1]xs + [0  0 ]ys + [4 ] >= [0 0]x + [0 1]xs + [0  0 ]ys + [4 ] = cons(x,app(xs,ys))
     
                     [1  10]     [12]    [0]        
     app(nil(),xs) = [0  0 ]xs + [4 ] >= [1] = nil()
    problem:
     strict:
      
     weak:
      app(cons(x,xs),ys) -> cons(x,app(xs,ys))
      app(nil(),xs) -> nil()
    Qed