In: John Mylopoulos; Raymond Reiter (Hrsg.). 12th International Joint Conference on Artificial Intelligence. International Joint Conference on Artificial Intelligence (IJCAI-91), 12th, August 24-30, Sydney, NSW, Australia, Pages 931-936, Vol. 2, Morgan Kaufmann, 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), August 24-30, Sydney, NSW, Australia, Pages 1003-1011, Morgan Kaufmann Publishers, 1991.