Waldemar Kocjan Per Kreuger Filtering Methods for Symmetric Cardinality Constraint. 200-208 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3011&spage=200 2004 conf/cpaior/2004 CPAIOR db/conf/cpaior/cpaior2004.html#KocjanK04