Non-uniform Cross-intersecting Families
Zhen Jia, Qing Xiang, Jimeng Xiao, H. X. Zhang · arXiv (Cornell University) · 2024
Let $m\geq 2$, $n$ be positive integers, and $R_i=\{k_{i,1} >k_{i,2} >\cdots> k_{i,t_i}\}$ be subsets of $[n]$ for $i=1,2,\ldots,m$. The families $\mathcal{F}_1\subseteq \binom{[n]}{R_1},\mathcal{F}_2\subseteq \binom{[n]}{R_2},\ldots,\mathcal{F}_m\subseteq \binom{[n]}{R_m}$ are said to be non-empty cross-intersecting if for each $i\in [m]$, $\mathcal{F}_i eq\emptyset$ and for any $A\in \mathcal{F}_i,B\in\mathcal{F}_j$, $1\leq i