@abc.abstractmethod<EOL><INDENT>def get_books_by_comment(self, comment_id):<DEDENT>
return<EOL>
Gets the list of ``Book`` objects mapped to a ``Comment``.

        :param comment_id: ``Id`` of a ``Comment``
        :type comment_id: ``osid.id.Id``
        :return: list of books
        :rtype: ``osid.commenting.BookList``
        :raise: ``NotFound`` -- ``comment_id`` is not found
        :raise: ``NullArgument`` -- ``comment_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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