Gerhard Brewka Answer Sets: From Constraint Programming Towards Qualitative Optimization. 34-46 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2923&spage=34 2004 conf/lpnmr/2004 LPNMR db/conf/lpnmr/lpnmr2004.html#Brewka04