Artur Czumaj Andrzej Lingas Johan Nilsson Improved Approximation Algorithms for Optimization Problems in Graphs with Superlogarithmic Treewidth. 544-553 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2906&spage=544 2003 conf/isaac/2003 ISAAC db/conf/isaac/isaac2003.html#CzumajLN03