English

Definable $(\omega, 2)$-theorem for families with VC-codensity less than $2$

Logic 2025-04-29 v3 Combinatorics

Abstract

Let S\mathcal{S} be a family of sets with VC-codensity less than 22. We prove that, if S\mathcal{S} has the (ω,2)(\omega, 2)-property (for any infinitely many sets in S\mathcal{S}, at least 22 among them intersect), then S\mathcal{S} can be partitioned into finitely many subfamilies, each with the finite intersection property. If S\mathcal{S} is definable in some first-order structure, then these subfamilies can be chosen definable too. This is a strengthening of the case q=2q=2 of the definable (p,q)(p,q)- conjecture in model theory and of the Alon-Kleitman-Matou\v{s}ek (p,q)(p,q)-theorem in combinatorics.

Keywords

Cite

@article{arxiv.2205.13665,
  title  = {Definable $(\omega, 2)$-theorem for families with VC-codensity less than $2$},
  author = {Pablo Andújar Guerrero},
  journal= {arXiv preprint arXiv:2205.13665},
  year   = {2025}
}

Comments

Proof streamlined after referee comments. I have two last names: And\'ujar Guerrero. ArXiV is currently unable to represent this and considers And\'ujar a middle name (when creating the BibTeX citation etc)

R2 v1 2026-06-24T11:30:17.709Z