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Random partition for Tokushige's $r$-wise intersecting conjecture

Combinatorics 2026-06-30 v1 Probability

Abstract

Let r3r\ge 3 and let 1>p1p2pn>01>p_1\ge p_2\ge\cdots\ge p_n>0. Let μp\mu_{\mathbf p} denote the product measure on 2[n]2^{[n]} where each coordinate ii is included independently with probability pip_i. A family A2[n]\mathcal A\subseteq 2^{[n]} is rr-wise intersecting if A1ArA_1\cap\cdots\cap A_r\neq\emptyset for all A1,,ArAA_1,\ldots,A_r\in\mathcal A. In 2022, Tokushige proved that if p2<r1rp_2<\frac{r-1}{r}, then every rr-wise intersecting family A2[n]\mathcal{A}\subseteq 2^{[n]} satisfies μp(A)p1\mu_{\mathbf p}(\mathcal{A})\le p_1, with equality only for stars centred at coordinates of maximum probability. He conjectured that the hypothesis p2<r1rp_2<\frac{r-1}{r} can be replaced by pr+1<r1rp_{r+1}<\frac{r-1}{r}. In this paper, we prove this conjecture in full. The key novelty is the introduction of a new random partition method, which reduces the problem to at most rr coordinates and solves it exactly, thereby fully covering all cases with multiple supercritical coordinates.

Cite

@article{arxiv.2606.31075,
  title  = {Random partition for Tokushige's $r$-wise intersecting conjecture},
  author = {Yongjiang Wu and Lihua Feng},
  journal= {arXiv preprint arXiv:2606.31075},
  year   = {2026}
}

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10 pages