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

From papers

Let [n]={1,,n}[n]=\{1,\ldots,n\} and let F2[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 A1ApA_1\subsetneq\cdots\subsetneq A_p and B1BqB_1\subsetneq\cdots\subsetneq B_q with A1B1=A_1\cap B_1=\emptyset. For 1in1\leq i\leq n, define

Fq(i)={F2[n]:1F, Fi}{F2[n]:iq+1Fi}.\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 p1p-1 levels.

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

Fmax{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 pqp\geq q, providing the proposed extremal construction. No resolution of this conjecture is stated in the supplied text.

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Sources & referencesView supporting material

Primary source

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

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