Kenneth L. Clarkson Herbert Edelsbrunner Leonidas J. Guibas Micha Sharir Emo Welzl Combinatorial Complexity Bounds for Arrangement of Curves and Spheres. 99-160 1990 5 Discrete & Computational Geometry db/journals/dcg/dcg5.html#ClarksonEGSW90 http://dx.doi.org/10.1007/BF02187783