Yong Luo Zhaohui Luo Combining Incoherent Coercions for Sigma-Types. 276-292 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3085&spage=276 2003 conf/types/2003 TYPES db/conf/types/types2003.html#LuoL03