Roberto Asín Robert Nieuwenhuis Albert Oliveras Enric Rodríguez-Carbonell Efficient Generation of Unsatisfiability Proofs and Cores in SAT. 16-30 2008 LPAR http://dx.doi.org/10.1007/978-3-540-89439-1_2 conf/lpar/2008 db/conf/lpar/lpar2008.html#AsinNOR08