Tomas Hruska Petr Kolencik Michal Mácel Behavioral Safety in a Model With Multiple Class Objects. 360-370 http://link.springer.de/link/service/series/0558/bibs/1521/15210360.htm 1998 conf/sofsem/1998 SOFSEM db/conf/sofsem/sofsem1998.html#HruskaKM98