Yves Moinard Unifying various approaches to constructive defaults , Rennes, France , oct , 1992 , Document Abstract Default logic is one of the most popular non monotonic formalisms. We show how the classical fix-point definitions of default extensions can be split into a first constructive stage, giving some kind of pre-extensions, and a final stability test. The notion of default reasoning obtained from the pre-extensions has a great interest on its own. It is proved to be equivalent to the notion defined by various authors, among them is the well known proposal of \L ukaszewicz. Some modal proposals can also be conveniently studied in this way. So, this text provides constructive definitions of various interesting kinds of pre-extensions. Moreover it shows how a number of already made proposals, including some modal ones, are closely related together even if they look very different. 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