Extremal-family conjecture for non-star intersecting s-stable families

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Let k≥4k\geq 4, let ([n]k)s-stable\binom{[n]}{k}_{s\text{-stable}} be the family of ss-stable kk-subsets of [n][n], and let F\mathcal{F} be a family in this set. An intersecting family is one whose members pairwise intersect; it is a non-star family if it is not contained in a family of all sets containing a fixed element. Let τ(F)\tau(\mathcal{F}) denote its covering number. For x∈[n]x\in[n] and Y∈([n]k)s-stableY\in\binom{[n]}{k}_{s\text{-stable}} with x∉Yx\notin Y, define

Fs,k(x,Y)={Y}∪{F∈([n]k)s-stable∣x∈F, F∩Y≠∅},\mathcal{F}_{s,k}(x,Y)=\{Y\}\cup\{F\in\binom{[n]}{k}_{s\text{-stable}}\mid x\in F,\ F\cap Y\neq\emptyset\},

and let Gs,k\mathcal{G}_{s,k} be the collection of all such families.

Extremal-family conjecture. If F⊆([n]k)s-stable\mathcal{F}\subseteq\binom{[n]}{k}_{s\text{-stable}} is a non-star intersecting family with τ(F)≥2\tau(\mathcal{F})\geq 2, then, for nn large enough—suggested in the source as n≥k(2s−1)+1n\geq k(2s-1)+1—

∣F∣≤max⁡{∣F∣∣F∈Gs,k}.|\mathcal{F}|\leq\max\{|F|\mid F\in\mathcal{G}_{s,k}\}.

This is an extremal set-theoretic conjecture intended to identify the largest non-star intersecting families of ss-stable sets. The source gives only a suggested threshold and does not provide a resolution.

References

Primary source

Wei-Chia Chen, Alex Parker and Shira Zerbib, “The chromatic number of 3-stable Kneser graphs”, arXiv:2607.12912 (2026).

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