1. Lecture Notes in Artificial Intelligence;C. Anger,2002
2. Apt, K., Blair, H., Walker, A.: Towards a theory of declarative knowledge. In: Minker, J. (ed.) Foundations of Deductive Databases and Logic Programming, pp. 89–148. Morgan Kaufmann, San Francisco (1987)
3. Brignoli, G., Costantini, S., D’Antona, O., Provetti, A.: Characterizing and computing stable models of logic programs: the non-stratified case. In: Baral, C., Mohanty, H. (eds.) Proceedings of the Conference on Information Technology, Bhubaneswar, India, pp. 197–201. AAAI Press, Menlo Park (1999)
4. Dimopoulos, Y., Torres, A.: Graph theoretical structures in logic programs and default theories. Theoretical Computer Science 170, 209–244 (1996)
5. Lecture Notes in Computer Science;T. Eiter,1997