Jian Guo Jungang Han Naiyong Jin Witness and Counter-Example on 3-Valued Model Checking. 633-637 2008 FSKD (2) http://dx.doi.org/10.1109/FSKD.2008.589 conf/fskd/2008-2 db/conf/fskd/fskd2008-2.html#GuoHJ08