Cross-intersecting family
= Cross-intersecting family
Two set families $\mathcal A$ and $\mathcal B$ are cross-intersecting when $A\cap B\ne\varnothing$ for every $A\in\mathcal A$ and $B\in\mathcal B$.
= Cross-intersecting family
Two set families $\mathcal A$ and $\mathcal B$ are cross-intersecting when $A\cap B\ne\varnothing$ for every $A\in\mathcal A$ and $B\in\mathcal B$.