@abc.abstractmethod<EOL><INDENT>def register_for_changed_grade_systems(self):<DEDENT>
pass<EOL>
Registers for notification of updated grade systems.

        ``GradeSystemReceiver.changedGradeSystems()`` is invoked when a
        system is changed or grades are changed within it.

        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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