def _is_permitted(self, identifiers, permission_s):
        """
        :type identifiers:  subject_abcs.IdentifierCollection

        :param permission_s: a collection of 1..N permissions
        :type permission_s: List of permission string(s)
        """

        for realm in self.realms:
            # the realm's is_permitted returns a generator
            yield from realm.is_permitted(identifiers, permission_s)