M. Gelfond, und V. Lifschitz. Proceedings of the Fifth International Conference on Logic Programming, Seite 1070--1080. Cambridge, Massachusetts, The MIT Press, (1988)
G. Brewka. Principles of Knowledge Representation and Reasoning: Proceedings of the Ninth International Conference (KR2004), Whistler, Canada, June 2-5, 2004, Seite 213--223. AAAI Press, (2004)