Frankl–Kupavskii conjecture for the shifted family P(m,s,ℓ)\mathcal P(m,s,\ell)

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Let n=s(m+1)−ℓn=s(m+1)-\ell and define

P(m,s,ℓ)={F⊆[n] ⁣:∣F∣+∣F∩[ℓ−1]∣≥m+1}.\mathcal P(m,s,\ell)=\{F\subseteq[n]\colon |F|+|F\cap[\ell-1]|\ge m+1\}.

For s≥2s\ge2, m≥1m\ge1, and 1≤ℓ≤⌈s/2⌉1\le\ell\le\lceil s/2\rceil, this family is a weighted construction with matching number less than ss. Frankl–Kupavskii conjecture. Suppose that s≥2s\ge2, m≥1m\ge1, and n=s(m+1)−ℓn=s(m+1)-\ell for some ℓ\ell with 1≤ℓ≤⌈s/2⌉1\le\ell\le\lceil s/2\rceil. Then

e(n,s)=∣P(m,s,ℓ)∣.e(n,s)=|\mathcal P(m,s,\ell)|.

The source reports proofs in several ranges, including asymptotic ranges of ℓ\ell, but does not state a complete resolution.

References

Primary source

Cheng Chi and Yan Wang, “Extremal Families for the Erdős–Kleitman Problem: The Missing Constructions”, arXiv:2607.25611 (2026).

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