@abc.abstractmethod<EOL><INDENT>def get_superseded_date(self):<DEDENT>
return<EOL>
Gets the date of an event to replace if a recurring event is offered on that date.

        :return: the date of the event to replace
        :rtype: ``osid.calendaring.DateTime``
        :raise: ``IllegalState`` -- ``supersedes_by_date()`` is ``false``

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