In: J. G. Neal; S. M. Walter (Hrsg.). Natural Language Processing Systems Workshop: Final Technical Report. Pages 79-96, RL-TR, Vol. 91-362, Rome Laboratory, New York, 1991.
In: John Mylopoulos; Raymond Reiter (Hrsg.). Proceedings of the 12th International Joint Conference on Artificial Intelligence. International Joint Conference on Artificial Intelligence (IJCAI-91), 12th, August 24-30, Sydney, NSW, Australia, Pages 1024-1030, Vol. 2, Morgan Kaufmann Publishers, 1991.