Doron Bustan Alon Flaisher Orna Grumberg Orna Kupferman Moshe Y. Vardi Regular Vacuity. 191-206 2005 conf/charme/2005 CHARME http://dx.doi.org/10.1007/11560548_16 db/conf/charme/charme2005.html#BustanFGKV05