Gábor Megyesi Frank Sottile Thorsten Theobald Common Transversals and Tangents to Two Lines and Two Quadrics in P. 543-571 2003 30 Discrete & Computational Geometry 4 http://dx.doi.org/10.1007/s00454-003-0789-4 db/journals/dcg/dcg30.html#MegyesiST03