@abc.abstractmethod<EOL><INDENT>def get_event_notification_session(self, event_receiver):<DEDENT>
return<EOL>
Gets the notification session for notifications pertaining to event changes.

        :param event_receiver: the event receiver
        :type event_receiver: ``osid.calendaring.EventReceiver``
        :return: an ``EventNotificationSession``
        :rtype: ``osid.calendaring.EventNotificationSession``
        :raise: ``NullArgument`` -- ``event_receiver`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_event_notification()`` is ``false``

        *compliance: optional -- This method must be implemented if
        ``supports_event_notification()`` is ``true``.*