1. Lecture Notes in Artificial Intelligence;C. Anger,2001
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 Publishers, San Francisco (1987)
3. Apt, K.R., Bol, R.N.: Logic programming and negation: A survey. Journal of Logic Programming 19/20, 9–71 (1994)
4. Asparagus,
http://asparagus.cs.uni-potsdam.de
5. Lecture Notes in Artificial Intelligence;A. Bösel,2004