@abc.abstractmethod<EOL><INDENT>def get_top_references(self, max_):<DEDENT>
return<EOL>
Gets the top rated references in this book.

        :param max: the maximum number to return
        :type max: ``cardinal``
        :return: the top references
        :rtype: ``osid.id.IdList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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