Vida Dujmovic Ken-ichi Kawarabayashi Bojan Mohar David R. Wood Improved upper bounds on the crossing number. 375-384 2008 Symposium on Computational Geometry http://doi.acm.org/10.1145/1377676.1377739 conf/compgeom/2008 db/conf/compgeom/compgeom2008.html#DujmovicKMW08