Nicola Galesi Neil Thapen The Complexity of Treelike Systems over lamda-Local Formulae. 68-74 2004 conf/coco/2004 IEEE Conference on Computational Complexity http://csdl.computer.org/comp/proceedings/ccc/2004/2120/00/21200068abs.htm db/conf/coco/coco2004.html#GalesiT04