Dietmar Ebner Gunnar W. Klau René Weiskircher Label Number Maximization in the Slider Model. 144-154 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3383&spage=144 2004 conf/gd/2004 Graph Drawing db/conf/gd/gd2004.html#EbnerKW04