Jan Maluszynski Andrzej Szalas Aida Vitória Paraconsistent Logic Programs with Four-Valued Rough Sets. 41-51 2008 RSCTC http://dx.doi.org/10.1007/978-3-540-88425-5_5 conf/rsctc/2008 db/conf/rsctc/rsctc2008.html#MaluszynskiSV08