Stephen J. H. Yang Alex S. Lee William C. Chu Hongji Yang Rule Base Verification Using Petri Nets. 476-485 1998 conf/compsac/1998 COMPSAC http://doi.ieeecomputersociety.org/10.1109/CMPSAC.1998.716699 db/conf/compsac/compsac1998.html#YangLCY98