Thomas Mailund Michael Westergaard Obtaining Memory-Efficient Reachability Graph Representations Using the Sweep-Line Method. 177-191 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2988&spage=177 2004 conf/tacas/2004 TACAS db/conf/tacas/tacas2004.html#MailundW04