@abc.abstractmethod<EOL><INDENT>def assign_offset_event_to_calendar(self, offset_event_id, calendar_id):<DEDENT>
pass<EOL>
Adds an existing ``OffsetEvent`` to a ``Calendar``.

        :param offset_event_id: the ``Id`` of the ``OffsetEvent``
        :type offset_event_id: ``osid.id.Id``
        :param calendar_id: the ``Id`` of the ``Calendar``
        :type calendar_id: ``osid.id.Id``
        :raise: ``AlreadyExists`` -- ``offset_event_id`` is already assigned to ``calendar_id``
        :raise: ``NotFound`` -- ``offset_event_id`` or ``calendar_id`` not found
        :raise: ``NullArgument`` -- ``offset_event_id`` or ``calendar_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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