@abc.abstractmethod<EOL><INDENT>def get_root_agencies(self):<DEDENT>
return<EOL>
Gets the root agencies in this agency hierarchy.

        :return: the root agencies
        :rtype: ``osid.authentication.AgencyList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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