Conjecture on totally chain-intersecting families for p at least q

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Let [n]={1,…,n}[n]=\{1,\ldots,n\} and let F⊆2[n]\mathcal F\subseteq 2^{[n]} be a family. For positive integers pp and qq, call F\mathcal F totally (p,q)(p,q)-chain intersecting if it contains no chains A1⊊⋯⊊ApA_1\subsetneq\cdots\subsetneq A_p and B1⊊⋯⊊BqB_1\subsetneq\cdots\subsetneq B_q with A1∩B1=∅A_1\cap B_1=\emptyset. For 1≤i≤n1\leq i\leq n, define

Fq(i)={F⊆2[n]:1∈F, ∣F∣≤i}∪{F⊆2[n]:i−q+1≤∣F∣≤i}.\mathcal F_q(i)=\{F\subseteq 2^{[n]}:1\in F,\ |F|\leq i\}\cup\{F\subseteq 2^{[n]}:i-q+1\leq |F|\leq i\}.

Let R\mathcal R denote the middle p−1p-1 levels.

Conjecture for totally chain-intersecting families. If F\mathcal F is a totally (p,q)(p,q)-chain intersecting family and p≥qp\geq q, then

∣F∣≤max⁡{∣Fq(i)∣,∣R∣}.|\mathcal F|\leq\max\{ |\mathcal F_q(i)|,|\mathcal R|\}.

The source explains that Fq(i)\mathcal F_q(i) is totally (p,q)(p,q)-chain intersecting when p≥qp\geq q, providing the proposed extremal construction. No resolution of this conjecture is stated in the supplied text.

References

Primary source

Dániel Gerbner, “A note on strongly and totally chain intersecting families”, arXiv:2302.05514 (2023).

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