Salem Benferhat Didier Dubois Henri Prade Possibilistic and Standard Probabilistic Semantics of Conditional Knowledge. 70-75 1997 conf/aaai/1997 AAAI/IAAI db/conf/aaai/aaai97.html#BenferhatDP97 http://www.aaai.org/Library/AAAI/1997/aaai97-011.php