Stéphane Grandcolas Laurent Henocque Nicolas Prcovic A Canonicity Test for Configuration. 853-857 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2833&spage=853 2003 conf/cp/2003 CP db/conf/cp/cp2003.html#GrandcolasHP03