def get_activity_notification_session(self, activity_receiver, proxy):
raise Unimplemented()<EOL>
Gets the notification session for notifications pertaining to activity changes.

        :param activity_receiver: the activity receiver
        :type activity_receiver: ``osid.learning.ActivityReceiver``
        :param proxy: a proxy
        :type proxy: ``osid.proxy.Proxy``
        :return: an ``ActivityNotificationSession``
        :rtype: ``osid.learning.ActivityNotificationSession``
        :raise: ``NullArgument`` -- ``activity_receiver`` or ``proxy`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_activity_notification()`` is ``false``

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