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arXiv 2608.00861math.CO

当 $n\ge 2k+3$ 时,集合的相交族通常是平凡的

Intersecting families of sets are usually trivial for $n\ge 2k+3$

Jiabao Yang

AI总结:

本文证明当 $n\ge 2k+3$ 时,几乎所有 $k$ 元均匀相交族都是平凡的,验证了Balogh等人的相关猜想,改进了此前的相交族研究结论。

AI中文摘要:

集合 $[n]$ 的子集族若不含任意两个不相交的集合,则称为相交族;若其所有成员都包含某个公共元素,则称为平凡族。Frankl与Kupavskii,以及Balogh、Das、Liu、Sharifzadeh和Tran分别独立证明,存在常数 $c>0$,当 $n\geq 2k+2+c\sqrt{k\ln k}$ 时,几乎所有 $k$ 元均匀相交族都是平凡的。Balogh、Garcia、Li和Wagner后续将该范围改进为 $n \geq 2k+100\ln k$。本文证明,对于所有 $n\geq 2k+3$,上述结论均成立,从而在该范围内验证了Balogh等人猜想的结论。

英文摘要:

A family of subsets of $[n]$ is called intersecting if it contains no pair of disjoint sets. It is called trivial if all its members contain a common element. Frankl and Kupavskii, and independently Balogh, Das, Liu, Sharifzadeh, and Tran, proved that there is a constant $c>0$ such that, whenever $n \geq 2k+2+c\sqrt{k\ln k}$, almost all $k$-uniform intersecting families are trivial. Balogh, Garcia, Li, and Wagner later improved this range to $n \geq 2k+100\ln k$. In this paper, we prove that the same conclusion holds for every $n\geq 2k+3$. This verifies the conjectured conclusion of Balogh, Garcia, Li, and Wagner throughout this range.

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