code: def split_layers(lower, upper, __fval=None, **fval):
      
      if __fval is not None:
          fval.update(__fval)
      split_bottom_up(lower, upper, **fval)
      split_top_down(lower, upper, **fval)
docs: Split 2 layers previously bound.
      This call un-links calls bind_top_down and bind_bottom_up. It is the opposite of  # noqa: E501
      bind_layers.
  
      Please have a look at their docs:
       - help(split_bottom_up)
       - help(split_top_down)