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)
T. Syrjänen. Helsinki University of Technology, Faculty of Information and Natural Sciences, Department of Information and Computer Science, Espoo, Finland, Doctoral dissertation, TKK Dissertations in Information and Computer Science TKK-ICS-D12, (2009)