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arXiv · 2605.01768

Hypergraph extensions of the Alon--Frankl Theorem and rainbow Turán problems

Xiamiao Zhao·Yuanpei Wang·Junpeng Zhou
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Abstract

Given a graph $F$, the $r$-expansion $F^{(r)+}$ of $F$ is the $r$-uniform hypergraph obtained from $F$ by inserting $r-2$ new distinct vertices in each edge of $F$. Recently, Alon and Frankl (JCTB, 2024) and Gerbner (JGT, 2023) studied the maximum number of edges in $n$-vertex $F$-free graphs with bounded matching number, respectively. Gerbner, Tompkins and Zhou (EJC, 2025) considered the analogous Turán problems on hypergraphs with bounded matching number. In this paper, we study hypergraph extensions of the Alon--Frankl Theorem. More precisely, we determine the maximum number of hyperedges in an $n$-vertex $r$-uniform hypergraph containing neither a matching $M^r_{s+1}$ nor the expansion $K_{\ell+1}^{(r)+}$ of the clique $K_{\ell+1}$ for all small $s<\frac{\ell^2-1}{2}$ and all sufficiently large $s$, respectively. This result partly confirms a conjecture proposed by Gerbner, Tompkins and Zhou (EJC, 2025). As a key tool, we determine the rainbow hyper-Turán number for expansions of cliques, which is defined as the maximum sum of size of a sequence of hypergraphs $\mathcal{H}_1,\dots,\mathcal{H}_k$ that contains no rainbow copies of expansions of cliques with given size. It extends the result of Keevash, Saks, Sudakov and Verstra{ë}te (AAM, 2004), which determined the rainbow Turán number of cliques in the graph case. These results shows a correlation between the hyper-Turán problem and the rainbow hyper-Turán number.

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Xiamiao Zhao, Yuanpei Wang, Junpeng Zhou. 2026-05-12. Hypergraph extensions of the Alon--Frankl Theorem and rainbow Turán problems. https://arxiv.org/abs/2605.01768

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