Michael R. Fellows Stefan Szeider Graham Wrightson On Finding Short Resolution Refutations and Small Unsatisfiable Subsets. 223-234 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3162&spage=223 2004 conf/iwpec/2004 IWPEC db/conf/iwpec/iwpec2004.html#FellowsSW04