Dusko Pavlovic Peter Pepper Douglas R. Smith Colimits for Concurrent Collectors. 568-597 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2772&spage=568 2003 conf/birthday/2003manna Verification: Theory and Practice db/conf/birthday/Manna2003.html#PavlovicPS03