We give a simple argument showing that the number of edges in the
intersection graph G of a family of n sets in the plane with a linear
union-complexity is O(ω(G)n). In particular, we prove χ(G)≤col(G)<19ω(G) for intersection graph G of a family of
pseudo-discs, which improves a previous bound.Comment: background and related work is now more complete; presentation
improve