def is_new_namespace_preorder( self, namespace_id_hash, lastblock=None ):
        """
        Given a namespace preorder hash, determine whether or not is is unseen before.
        """
        if lastblock is None:
            lastblock = self.lastblock 

        preorder = namedb_get_namespace_preorder( self.db, namespace_id_hash, lastblock )
        if preorder is not None:
            return False 
        else:
            return True
Given a namespace preorder hash, determine whether or not is is unseen before.