1. Gabbay, D.: What is negation as failure? (1985) (manuscript)
2. Lloyd, J.W.: Foundations of Logic Programming, 2nd edn. Springer, Heidelberg (1987)
3. Clark, K.: Negation as failure (Originally published in 1978); reproduced in Readings in nonmonotonic reasoning, pp. 311–325. Morgan Kaufmann Publishers (1987)
4. Gabbay, D.: An Equational Approach to Argumentation Networks, p. 107 (February 2011); to appear in Argumentation and Computation
5. Lecture Notes in Computer Science;D.M. Gabbay,2011