Riccardo Rosati Reasoning with Minimal Belief and Negation as Failure: Algorithms and Complexity. 430-435 1997 conf/aaai/1997 AAAI/IAAI db/conf/aaai/aaai97.html#Rosati97 http://www.aaai.org/Library/AAAI/1997/aaai97-066.php