More on Representation Theory for Default Logic

AbstractIn this paper, we investigate the representability of a family of theories as the set of extensions of a default theory. First, we present both new necessary conditions and sufficient ones for the representability by means of general default theories, which improves on similar results known before. Second, we show that one always obtains representable families by eliminating countably many theories from a representable family. Finally, we construct two examples of denumerable, representable families; one is not supercompactly nonincluding, and the other consists of mutually inconsistent theories but fails to be represented by a normal default theory