K. Lochbaum, B. Grosz, and C. Sidner. Proceedings of the Eighth National Conference on Artificial Intelligence, page 485-490. Menlo Park, California, AAAI Press, (1990)
R. Schank, and R. Abelson. Thinking: Readings in Cognitive Science, Proceedings of the Fourth International Joint Conference on Artificial Intelligence, page 151-157. Tbilisi, USSR, (1975)