Reseaux électriques planaires II. Y. de Colin de Verdière; I. Gitler — 1996 Commentarii mathematici Helvetici
The crossing number of a projective graph is quadratic in the face-width. Gitler, I.; Hlineny, P.; Leaños, J.; Salazar, G. — 2008 The Electronic Journal of Combinatorics [electronic only]