Rajeev Kohli Ramesh Krishnamurti Prakash Mirchandani The Minimum Satisfiability Problem. 275-283 1994 7 SIAM J. Discrete Math. 2 http://epubs.siam.org/sam-bin/dbq/article/22083 db/journals/siamdm/siamdm7.html#KohliKM94