English

A few new oddtown and eventown problems

Combinatorics 2025-03-27 v3

Abstract

Given a vector α=(α1,,αk)F2k\alpha = (\alpha_1, \ldots, \alpha_k) \in \mathbb{F}_2^k, we say a collection of subsets F\mathcal{F} satisfies α\alpha-intersection pattern modulo 22 if all ii-wise intersections consisting of ii distinct sets from F\mathcal{F} have size αi(mod2)\alpha_i \pmod{2}. In this language, the classical oddtown and eventown problems correspond to vectors α=(1,0)\alpha=(1,0) and α=(0,0)\alpha=(0,0) respectively. In this paper, we determine the largest such set families of subsets on a nn-element set with α\alpha-intersection pattern modulo 22 for all αF23\alpha \in \mathbb{F}_2^3 and all αF24\alpha \in \mathbb{F}_2^4 asymptotically. Lastly, we consider the corresponding problem with restrictions modulo 33.

Keywords

Cite

@article{arxiv.2312.13588,
  title  = {A few new oddtown and eventown problems},
  author = {Griffin Johnston and Jason O'Neill},
  journal= {arXiv preprint arXiv:2312.13588},
  year   = {2025}
}

Comments

revisions from referee report

R2 v1 2026-06-28T13:58:20.597Z