TY - JOUR

T1 - A new lower bound on hadwiger-debrunner numbers in the plane

AU - Keller, C.

AU - Smorodinsky, S.

N1 - Funding Information:
Received June 7, 2019. 2010 Mathematics Subject Classification. Primary 52A37, 05D40. The first author was supported by Grants 409/16 and 635/16 from the Israel Science Foundation, by the Shulamit Aloni Post-Doctoral Fellowship of the Israel Ministry of Science and Technology, and by a Kreitman Foundation Post-Doctoral Fellowship. The second author was supported by Grant 635/16 from the Israel Science Foundation.
Publisher Copyright:
© 2019, Univerzita Komenskeho. All rights reserved.

PY - 2019/9/2

Y1 - 2019/9/2

N2 - A family of sets F is said to satisfy the (p, q)-property if among any p sets in F some q have a non-empty intersection. Hadwiger and Debrunner (1957) conjectured that for any p ≥ q ≥ d +1 there exists c = cd(p, q), such that any family of compact convex sets in that satisfies the (p, q)-property can be pierced by at most c points. In a celebrated result from 1992, Alon and Kleitman proved the conjecture. However, obtaining sharp bounds on cd(p, q), known as the ‘the Hadwiger-Debrunner numbers,’ is still a major open problem in combinatorial geometry. The best currently known lower bound on the Hadwiger-Debrunner numbers in the plane is c2(image, found), while the best known upper bound is O(image, found). In this paper we improve the lower bound significantly by showing that c2 (p, q) ≥ p1+Ω (1/q). Furthermore, the bound is obtained by a family of lines and is tight for all families that have a bounded VC-dimension. Unlike previous bounds on the Hadwiger-Debrunner numbers, which mainly used the weak epsilon-net theorem, our bound stems from a surprising connection of the (p, q)-problem to an old problem of Erdos on points in general position in the plane. We use a novel construction for the Erdos’ problem, obtained recently by Balogh and Solymosi using the hypergraph container method, to get the lower bound on c2 (p, 3). We then generalize the bound to c2(p, q) for any q ≥ 3.

AB - A family of sets F is said to satisfy the (p, q)-property if among any p sets in F some q have a non-empty intersection. Hadwiger and Debrunner (1957) conjectured that for any p ≥ q ≥ d +1 there exists c = cd(p, q), such that any family of compact convex sets in that satisfies the (p, q)-property can be pierced by at most c points. In a celebrated result from 1992, Alon and Kleitman proved the conjecture. However, obtaining sharp bounds on cd(p, q), known as the ‘the Hadwiger-Debrunner numbers,’ is still a major open problem in combinatorial geometry. The best currently known lower bound on the Hadwiger-Debrunner numbers in the plane is c2(image, found), while the best known upper bound is O(image, found). In this paper we improve the lower bound significantly by showing that c2 (p, q) ≥ p1+Ω (1/q). Furthermore, the bound is obtained by a family of lines and is tight for all families that have a bounded VC-dimension. Unlike previous bounds on the Hadwiger-Debrunner numbers, which mainly used the weak epsilon-net theorem, our bound stems from a surprising connection of the (p, q)-problem to an old problem of Erdos on points in general position in the plane. We use a novel construction for the Erdos’ problem, obtained recently by Balogh and Solymosi using the hypergraph container method, to get the lower bound on c2 (p, 3). We then generalize the bound to c2(p, q) for any q ≥ 3.

UR - http://www.scopus.com/inward/record.url?scp=85073773771&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:85073773771

VL - 88

SP - 855

EP - 860

JO - Acta Mathematica Universitatis Comenianae

JF - Acta Mathematica Universitatis Comenianae

SN - 0862-9544

IS - 3

ER -