code: def _delete_single_relation(self, src, relation, dst):
          ''' deletes a single relation between objects '''
          self.__require_string__(relation)
          src_id = self._id_of(src)
          dst_id = self._id_of(dst)
          with self._write_lock:
              self._execute('''
                  DELETE from relations where src=? and name=? and dst=?
              ''', (src_id, relation, dst_id))
              self.autocommit(f _delete_single_relation(self, src, relation, dst):
          ''' deletes a single relation between objects '''
          self.__require_string__(relation)
          src_id = self._id_of(src)
          dst_id = self._id_of(dst)
          with self._write_lock:
              self._execute('''
                  DELETE from relations where src=? and name=? and dst=?
              ''', (src_id, relation, dst_id))
              self.autocommit()
docs: deletes a single relation between objects