docs: def orderby(cls, ops, kwargs):
      """Re-order arguments via the class's ``order_key`` key object/function.
      Use this for commutative operations:
      E.g.::
  
          >>> class Times(Operation):
          ...     order_key = lambda val: val
          ...     simplifications = [orderby, ]
          >>> Times.create(2,1)
          Times(1, 2)
      """
      return sorted(ops, key=cls.order_key), kwargs