## Abstract

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.

Original language | English |
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Article number | 105236 |

Journal | Journal of Combinatorial Theory. Series A |

Volume | 173 |

DOIs | |

State | Published - 1 Jul 2020 |

Externally published | Yes |

## Keywords

- Empty k-gon
- Empty pentagon
- Erdös–Szekeres type problem
- Planar point set
- k-Hole

## ASJC Scopus subject areas

- Theoretical Computer Science
- Discrete Mathematics and Combinatorics
- Computational Theory and Mathematics