Modifications to Circumscription for Commonsense Reasoning.

Circumscription is one of the major formalizations of nonmonotonic reasoning. It however has several drawbacks. The first of thesee is that the circumscription of a satisfiable theory can sometimes be unsatisfiable. The second is that cirumscription does not deal well with equality. These problems can be overcome by redefining circumscription, and modifying the minimality criterion. Various different possibilities are considered, and some are shown to be equivalent.