Nele Smeets Eric Steegmans A Methodology for Writing Class Contracts. 418-422 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3381&spage=418 2005 conf/sofsem/2005 SOFSEM db/conf/sofsem/sofsem2005.html#SmeetsS05