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Niemelä, I.; Simons, P.; Soinenen, T. (2000). «Stable model semantics of weight constraint rules». En Gelfond, Michael; Leone, Nicole; Pfeifer, eds. Logic Programming and Nonmonotonic Reasoning: 5th International Conference, LPNMR '99, El Paso, Texas, USA, December 2–4, 1999 Proceedings. Lecture Notes in Computer Science: Lecture Notes in Artificial Intelligence 1730. Springer. pp. 317-331. ISBN978-3-540-66749-0.as Postscript