Improved bounds for the number of (≤ k)-sets, convex quadrilaterals, and the rectilinear crossing number of kn

  • Authors:
  • József Balogh;Gelasio Salazar

  • Affiliations:
  • Department of Mathematics, The Ohio State University, Columbus, OH;IICO-UASLP, San Luis Potosi, SLP, Mexico

  • Venue:
  • GD'04 Proceedings of the 12th international conference on Graph Drawing
  • Year:
  • 2004

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Abstract

We use circular sequences to give an improved lower bound on the minimum number of (≤ k)-sets in a set of points in general position. We then use this to show that if S is a set of n points in general position, then the number □(S) of convex quadrilaterals determined by the points in S is at least $0.37553\binom{n}{4} + O(n^3)$. This in turn implies that the rectilinear crossing number $\overline{\hbox{\rm cr}}(K_n)$ of the complete graph Kn is at least $0.37553\binom{n}{4} + O(n^3)$. These improved bounds refine results recently obtained by Ábrego and Fernández-Merchant, and by Lovász, Vesztergombi, Wagner and Welzl.