Conrado Martínez Xavier Molinero An Experimental Study of Unranking Algorithms. 326-340 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3059&spage=326 2004 conf/wea/2004 WEA db/conf/wea/wea2004.html#MartinezM04