Elmar Bihler Walter Vogler Timed Petri Nets: Efficiency of Asynchronous Systems. 25-58 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3185&spage=25 2004 conf/sfm/2004 SFM db/conf/sfm/sfm2004.html#BihlerV04