Uniform sets in a family with restricted intersections

Abstract

Let $\mathcal{F}$ be a family of subsets of $[n]=\{1,\dots ,n\}$ and let $L$ be a set of nonnegative integers. The family $\mathcal{F}$ is \emph{$L$-intersecting} if $|F\cap F^{\prime }|\in L$ for every two distinct members $F,F^{\prime }\in \mathcal{F}$; and $\mathcal{F}$ is $k$-uniform if all its members have the same size $k$. A large variety of problems and results in extremal set theory concern on $k$-uniform $L$-intersecting families. Many attentions are paid to finding the maximum size of a family among all $k$-uniform $L$-intersecting families with prescribed $n,k$ and $L$. In this paper, from another point of view, we propose and investigate the problem of estimating the maximum size of a member in a family among all uniform $L$-intersecting families with size $m$, here $n,m$ and $L$ are prescribed. Our results aim to find out more precise relations of $n,m,k$ and $L$.

18 pages