English

A note on infinite versions of $(p,q)$-theorems

Combinatorics 2024-12-06 v1

Abstract

We prove that fractional Helly and (p,q)(p,q)-theorems imply (0,q)(\aleph_0,q)-theorems in an entirely abstract setting. We give a plethora of applications, including reproving almost all earlier (0,q)(\aleph_0,q)-theorems about geometric hypergraphs that were proved recently. Some of the corollaries are new results, for example, we prove that if F\mathcal{F} is an infinite family of convex compact sets in Rd\mathbb{R}^d and among every 0\aleph_0 of the sets some d+1d+1 contain a point in their intersection with integer coordinates, then all the members of F\mathcal{F} can be hit with finitely many points with integer coordinates.

Keywords

Cite

@article{arxiv.2412.04066,
  title  = {A note on infinite versions of $(p,q)$-theorems},
  author = {Attila Jung and Dömötör Pálvölgyi},
  journal= {arXiv preprint arXiv:2412.04066},
  year   = {2024}
}

Comments

A previous version of this work appeared as part of arXiv:2311.15646 (v1 and v2). The main theorem is included there, but the current version provides a clearer presentation and additional applications