code: def element(self, inp=None):
          
          for set in self.sets:
              try:
                  return set.element(inp)
              except NotImplementedError:
                  pass
          raise NotImplementedError('`element` not implemented for any of the '
                                    'subsets')
docs: Create a new element.
  
          First tries calling the first set, then the second, etc.
  
          For more specific control, use ``set[i].element()`` to pick which
          subset to use.