Weighted Frankl conjecture for union-closed families

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Let [n]={1,…,n}[n]=\{1,\ldots,n\}, and let F⊆2[n]\mathcal{F}\subseteq 2^{[n]} be a non-empty union-closed family, meaning that A∪B∈FA\cup B\in\mathcal{F} for all A,B∈FA,B\in\mathcal{F}. Let x1,x2,…,xn≥1x_1,x_2,\ldots,x_n\geq1 be real numbers. Weighted Frankl conjecture. There exists k∈[n]k\in[n] such that

∑S∈F, k∈S∏m∈S, m≠kxm≥∑S∈F, k∉S∏m∈Sxm.\sum_{S\in\mathcal{F},\ k\in S}\prod_{m\in S,\ m\neq k}x_m\geq\sum_{S\in\mathcal{F},\ k\notin S}\prod_{m\in S}x_m.

This weighted assertion is motivated by blowing up each element into a family of non-empty subsets. The source presents it as a new conjecture derived from Frankl's conjecture, and gives no resolution; in particular, its general validity remains open.

References

Primary source

Veronica Phan, “Blow-up trick in Combinatorics”, arXiv:2605.06725 (2026).

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