Maximal $3$-wise intersecting families

Abstract

A family $\mathcal{F}$ on ground set $[n]:=\{1,2,\dots ,n\}$ is maximal $k$-wise intersecting if every collection of at most $k$ sets in $\mathcal{F}$ has non-empty intersection, and no other set can be added to $\mathcal{F}$ while maintaining this property. In 1974, Erdős and Kleitman asked for the minimum size of a maximal $k$-wise intersecting family. We answer their question for $k=3$ and sufficiently large $n$. We show that the unique minimum family is obtained by partitioning the ground set $[n]$ into two sets $A$ and $B$ with almost equal sizes and taking the family consisting of all the proper supersets of $A$ and of $B$.

17 pages. This is a combination of the results from arXiv:2110.12708 (version 1) and the results from arXiv:2206.09334, which settled the even and odd case of the problem, respectively