Sébastien Bornot Joseph Sifakis Stavros Tripakis Modeling Urgency in Timed Systems. 103-129 1997 conf/compos/1997 COMPOS http://link.springer.de/link/service/series/0558/bibs/1536/15360103.htm db/conf/compos/compos1997.html#BornotST97