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arXiv · 2312.13588

A few new oddtown and eventown problems

Griffin Johnston·Jason O'Neill
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Abstract

Given a vector $α= (α_1, \ldots, α_k) \in \mathbb{F}_2^k$, we say a collection of subsets $\mathcal{F}$ satisfies $α$-intersection pattern modulo $2$ if all $i$-wise intersections consisting of $i$ distinct sets from $\mathcal{F}$ have size $α_i \pmod{2}$. In this language, the classical oddtown and eventown problems correspond to vectors $α=(1,0)$ and $α=(0,0)$ respectively. In this paper, we determine the largest such set families of subsets on a $n$-element set with $α$-intersection pattern modulo $2$ for all $α\in \mathbb{F}_2^3$ and all $α\in \mathbb{F}_2^4$ asymptotically. Lastly, we consider the corresponding problem with restrictions modulo $3$.

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Griffin Johnston, Jason O'Neill. 2025-03-26. A few new oddtown and eventown problems. https://arxiv.org/abs/2312.13588

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