Handling contradictions in default theories

Reiter's default logic can not tolerate contradictions in default theories. In the paper we modify the definition of default extension to permit conflicts between justifications of used defaults and default conclusions, which are called incoherences, to ensure the existence of ex tension. Then desired extensions are selected as preferred ones according to the criterion that incoherences should be minimal in a, preferred extension. Besides, the underlying reasoning system is shifted to four-valued logic to deal with inconsistencies in axioms of default theories.Computer Science, Artificial IntelligenceComputer Science, Theory & MethodsEICPCI-S(ISTP)