Yves Moinard Reasoning by Cases without Contraposition in Default Logic , ECAI'94 (European Conf. on Artificial Intelligence) , Wiley , Amsterdam , 381--385 , aug , 1994 , The document available on this site is a modified version, made on April 25, 1995, after a remark by Chiaki Sakama. , Document Abstract Default logic, one of the best known formalisms to express common sense reasoning, does not allow to reason by cases in its standard formulations. We propose a natural and easy way of translating rules with exceptions into standard defaults, which allows to reason by cases without giving any unwanted contraposition. This solution is the simplest possible extension to the first coming idea consisting in taking the defaults by sets. Thus we keep the attractive simplicity of default logic basically intact. Our solution is independant of the notion of ``commitment" and can as well be applied to the versions of default logic caring about commitment. We provide several examples in order to make precise what is wanted. We study various other proposals in the literature, showing that either they give some kind of unwanted contraposition or that they need a new and non standard form of disjunction and that they greatly modify the notion of default reasoning. This web site is maintained by René Quiniou using the Weave system from the Caravel project: http://www-caravel.inria.fr. Last modification: 10-07-2011 09:54:25