Kristoffer Arnsfelt Hansen Constant Width Planar Branching Programs Characterize ACC^0 in Quasipolynomial Size. 92-99 2008 IEEE Conference on Computational Complexity http://doi.ieeecomputersociety.org/10.1109/CCC.2008.30 conf/coco/2008 db/conf/coco/coco2008.html#Hansen08