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arXiv · 2606.25931

A Simple Counting Argument for Dense Linear Hypergraphs

Lior Gishboliner·József Solymosi
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Abstract

In connection to the Brown-Erd\H{o}s-S\'os conjecture, we give a short local averaging proof of a density theorem for linear uniform hypergraphs. Let $r \ge 3$, $k \ge 3$, and suppose that $n \ge (r-2)(k-2)+1$. If $H$ is a linear $r$-uniform hypergraph on $n$ vertices and \[|E(H)| \geq \frac{k-2}{r^2((r-2)(k-2)+1)}n^2 + \frac{n}{r},\] then $H$ contains $k$ edges spanning at most $(r-2)k+3$ vertices. In the standard linear-density normalization, this gives the asymptotic density threshold $c \geq \frac{r-1}{r} \cdot \frac{k-2}{(r-2)(k-2)+1} + o(1)$. In particular, this yields a simple proof of the large-uniformity form of the Brown-Erd\H{o}s-S\'os theorem, due to Keevash and Long. In the case of triple systems, our bound becomes $c \geq \frac{2(k-2)}{3(k-1)} + o(1)$, improving upon a bound of $\frac{4}{5}$ due to Santos and Tyomkyn.

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Lior Gishboliner, József Solymosi. 2026-06-24. A Simple Counting Argument for Dense Linear Hypergraphs. https://arxiv.org/abs/2606.25931

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