Update the set, removing elements found in keeping only elements
        found in any of the *iterables*.

def difference_update(self, *iterables):
        """
        Update the set, removing elements found in keeping only elements
        found in any of the *iterables*.
        """
        _set = self._set
        values = set(chain(*iterables))
        if (4 * len(values)) > len(_set):
            _list = self._list
            _set.difference_update(values)
            _list.clear()
            _list.update(_set)
        else:
            _discard = self.discard
            for value in values:
                _discard(value)
        return self