Guy Even Sudipto Guha Baruch Schieber Improved Approximations of Crossings in Graph Drawings and VLSI Layout Areas. 231-252 2002 32 SIAM J. Comput. 1 http://epubs.siam.org/sam-bin/dbq/article/37352 db/journals/siamcomp/siamcomp32.html#EvenGS02