1. K. Apt and H.A. Blair. Arithmetical classification of perfect models of stratified programs. Fundamenta Informaticac, 12:1–17, 1990.
2. K. Apt, H.A. Blair, and A. Walker. Towards a theory of declarative knowledge. In J. Minker, editor, Foundations of Deductive Databases and Logic Programming, pages 89–142, Los Altos, CA, 1987. Morgan Kaufmann.
3. R. Ben-Eliyahu and R. Dechter. Propositional semantics for disjunctive logic programs. In K. Apt, editor, Proceedings of International Joint Conference and Symposium on Logic Programming, pages 813–827, Cambridge, MA, 1992, MIT Press.
4. N. Bidoit and Ch. Froidevaux. General logical databases and programs: Default logic semantics and stratification. Information and Computation, 91:15–54, 1991.
5. P. Gholewiński, W. Marek, A. Mikitiuk and M. Truszczyński. Experimenting with default logic In Proceedings of ICLP-95, MIT Press, to appear.