The Erdős–Ko–Rado-type conjecture for L-intersecting families

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Let 0<s≤k≤n0<s\leq k\leq n be positive integers. Let L={ℓ1,…,ℓs}L=\{\ell_1,\ldots,\ell_s\} be a set of ss positive integers such that 0<ℓ1<⋯<ℓs0<\ell_1<\cdots<\ell_s. Suppose that n>k2−k+1n>k^2-k+1. Let F={F1,…,Fm}\mathcal F=\{F_1,\ldots,F_m\} be an LL-intersecting, kk-uniform family of subsets of [n][n], meaning that ∣Fi∩Fj∣∈L|F_i\cap F_j|\in L for every distinct Fi,Fj∈FF_i,F_j\in\mathcal F. The Erdős–Ko–Rado-type conjecture for LL-intersecting families. Then

m≤(n−ℓ1s).m\leq {n-\ell_1\choose s}.

Moreover, if

∣F∣=(n−ℓ1s),|\mathcal F|={n-\ell_1\choose s},

then there exists a set T∈([n]ℓ1)T\in {[n]\choose \ell_1} such that T⊆FT\subseteq F for every F∈FF\in\mathcal F. This conjecture extends the preceding bound and its equality characterization from the proven range to the stated condition n>k2−k+1n>k^2-k+1; the projective-plane example motivating it shows why the threshold is natural. Its resolution is not indicated in the supplied text.

References

Primary source

Gábor Hegedüs, “A generalization of the Erdős-Ko-Rado Theorem”, arXiv:1512.05531 (2015).

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