Degenerate crossing numbers
János Pach, Gézá Tóth · 2006
Let G be a graph with n vertices and e ≥ 4n edges, drawn in the plane in such a way that if two or more edges (arcs) share an interior point p ,then they must properly cross one another at p. It is shown that the number of crossing points, counted without multiplicity, is at least constant times e and that the order of magnitude of this bound cannot be improved. If, in addition, two edges are allowed to cross only at most once, then the number of crossing points must exceed constant times (e/n)4.