1. Negation as failure in logic and database;Clark,1978
2. M. Gelfond (1987) On stratified autoepistemic theories AAAI 87.
3. R. Fagin, J. Halpern & M. Vardi A nonstandard approach to the logical omniscience problem TARK 88.
4. J. Halpern (1993) Reasoning about only knowing with many agents AAAI 93.
5. Knowledge and Belief;Hintikka,1962