YES

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

Proof:
 Matrix Interpretation Processor: dim=3
  
  interpretation:
                    [1 0 0]     [1 0 0]     [0]
   [cons](x0, x1) = [0 0 0]x0 + [0 0 0]x1 + [0]
                    [0 0 0]     [0 0 1]     [1],
   
                   [1 0 1]     [1 0 0]  
   [app](x0, x1) = [0 0 0]x0 + [0 0 0]x1
                   [0 0 1]     [0 0 0]  ,
   
           [0]
   [nil] = [0]
           [1]
  orientation:
                   [1 0 0]     [1]    [0]        
   app(nil(),xs) = [0 0 0]xs + [0] >= [0] = nil()
                   [0 0 0]     [1]    [1]        
   
                        [1 0 0]    [1 0 1]     [1 0 0]     [1]    [1 0 0]    [1 0 1]     [1 0 0]     [0]                     
   app(cons(x,xs),ys) = [0 0 0]x + [0 0 0]xs + [0 0 0]ys + [0] >= [0 0 0]x + [0 0 0]xs + [0 0 0]ys + [0] = cons(x,app(xs,ys))
                        [0 0 0]    [0 0 1]     [0 0 0]     [1]    [0 0 0]    [0 0 1]     [0 0 0]     [1]                     
  problem:
   
  Qed