Fülöp, János, Balázs Imreh, and Ferenc Friedler. “On the Reformulation of Some Classes of PNS-Problems As Set Covering Problems”. Acta Cybernetica 13, no. 3 (January 1, 1998): 329–337. Accessed April 2, 2025. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3495.