@abc.abstractmethod<EOL><INDENT>def get_sponsor_ids(self):<DEDENT>
return<EOL>
Gets the ``Id`` of the recurring event sponsors.

        :return: the sponsor ``Ids``
        :rtype: ``osid.id.IdList``
        :raise: ``IllegalState`` -- ``has_sponsors()`` is ``false``

        *compliance: mandatory -- This method must be implemented.*