Kung-Kiu Lau Mario Ornaghi Correct OO Systems in Computational Logic. 34-53 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3018&spage=34 2003 conf/lopstr/2003 LOPSTR db/conf/lopstr/lopstr2003.html#LauO03