Feodor F. Dragan Chenyu Yan Derek G. Corneil Collective Tree Spanners and Routing in AT-free Related Graphs. 68-80 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3353&spage=68 2004 conf/wg/2004 WG db/conf/wg/wg2004.html#DraganYC04