Exceptional-groups conjecture for intersecting Saxl-hypergraph edges

Let GSym(Ω)G\leq \operatorname{Sym}(\Omega) be a finite primitive permutation group with base size b(G)2b(G)\geq 2, and let H(G)\mathcal{H}(G) be its Saxl hypergraph. Exceptional-groups conjecture. Exactly one of the following holds: GG is Sn\operatorname{S}_n in its natural action with n4n\geq 4; GG is An\operatorname{A}_n in its natural action with n6n\geq 6; or, for every pair of distinct points α,βΩ\alpha,\beta\in\Omega, there exist edges Eα,EβE_\alpha,E_\beta of H(G)\mathcal{H}(G) such that αEα\alpha\in E_\alpha, βEβ\beta\in E_\beta, and EαEβ=1|E_\alpha\cap E_\beta|=1. The claim asserts that the symmetric and alternating natural actions are the only exceptions to this edge-intersection property; the supplied source gives no resolution.

Sources & referencesView supporting material

Primary source

Melissa Lee and Anthony Pisani, “The Saxl hypergraph of a permutation group”, arXiv:2505.13849 (2025).

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