code: def clone(orig, n):
      
      if n == 0:
          return layerize(noop())
      layers = [orig]
      for i in range(n - 1):
          layers.append(copy.deepcopy(orig))
          layers[-1].set_id()
      return FeedForward(layers)
docs: Construct `n` copies of a layer, with distinct weights.
  
      i.e. `clone(f, 3)(x)` computes `f(f'(f''(x)))`.