@abc.abstractmethod<EOL><INDENT>def get_repositories(self):<DEDENT>
return<EOL>
Gets all ``Repositories``.

        In plenary mode, the returned list contains all known
        repositories or an error results. Otherwise, the returned list
        may contain only those repositories that are accessible through
        this session.

        :return: a list of ``Repositories``
        :rtype: ``osid.repository.RepositoryList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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