Jan van Katwijk Hans Toetenel Abd-El-Kader Sahraoui Eric Anderson Janusz Zalewski Specification and Verification of a Safety Shell with Statecharts and Extended Timed Graphs. 37-52 http://link.springer.de/link/service/series/0558/bibs/1943/19430037.htm 2000 conf/safecomp/2000 SAFECOMP db/conf/safecomp/safecomp2000.html#KatwijkTSAZ00