# A superlinear lower bound on the number of 5-holes

Oswin Aichholzer, Martin Balko, Thomas Hackl, Jan Kyncl, Irene Parada, Manfred Scheucher (Corresponding author), Pavel Valtr, Birgit Vogtenhuber

## Samenvatting

Let P be a finite set of points in the plane in general position, that is, no three points of P are on a common line. We say that a set H of five points from P is a 5-hole in P if H is the vertex set of a convex 5-gon containing no other points of P. For a positive integer n, let h 5(n) be the minimum number of 5-holes among all sets of n points in the plane in general position. Despite many efforts in the last 30 years, the best known asymptotic lower and upper bounds for h 5(n) have been of order Ω(n) and O(n 2), respectively. We show that h 5(n)=Ω(nlog 4/5⁡n), obtaining the first superlinear lower bound on h 5(n). The following structural result, which might be of independent interest, is a crucial step in the proof of this lower bound. If a finite set P of points in the plane in general position is partitioned by a line ℓ into two subsets, each of size at least 5 and not in convex position, then ℓ intersects the convex hull of some 5-hole in P. The proof of this result is computer-assisted.

Originele taal-2 Engels 105236 31 Journal of Combinatorial Theory, Series A 173 https://doi.org/10.1016/J.JCTA.2020.105236 Gepubliceerd - jul 2020 Ja

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