Frankl--Wang conjecture for non-trivial cross-intersecting families of different uniformities

From papers

Let n2a2b4n\ge 2a\ge 2b\ge 4, and let A0([2,n]a)A_0\in\binom{[2,n]}{a} and B0([2,n]b)B_0\in\binom{[2,n]}{b} satisfy A0B0A_0\cap B_0\ne\emptyset. Define

A0={A0}{A([n]a):1A, AB0},\mathcal{A}_0=\{A_0\}\cup\{A\in\binom{[n]}{a}:1\in A,\ A\cap B_0\ne\emptyset\}, B0={B0}{B([n]b):1B, BA0}.\mathcal{B}_0=\{B_0\}\cup\{B\in\binom{[n]}{b}:1\in B,\ B\cap A_0\ne\emptyset\}.

Two families are cross-intersecting if every member of one intersects every member of the other, and are non-trivial if neither family is a star. Frankl--Wang's conjecture. If A([n]a)\mathcal{A}\subset\binom{[n]}{a} and B([n]b)\mathcal{B}\subset\binom{[n]}{b} are non-trivial cross-intersecting families, then

ABA0B0.|\mathcal{A}||\mathcal{B}|\le |\mathcal{A}_0||\mathcal{B}_0|.

This proposes the cross-Hilton--Milner-type pair as the extremal construction when the two families have different uniformities. The supplied source does not state whether the conjecture has been resolved.

Progress summary

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Sources & referencesView supporting material

Primary source

Yang Huang, “A sharp product bound for non-trivial cross-intersecting families”, arXiv:2606.23322 (2026).

Solutions 0

No solutions have been posted yet.