Alberto Ciaffaglione Luigi Liquori Marino Miculan Imperative Object-Based Calculi in Co-inductive Type Theories. 59-77 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2850&spage=59 2003 conf/lpar/2003 LPAR db/conf/lpar/lpar2003.html#CiaffaglioneLM03