Conjecture on the extremal obstruction to perfect matchings

Let HH be a 3-graph of order nn, let σ2(H)\sigma_2(H) denote the minimum deg(u)+deg(v)\deg(u)+\deg(v) over adjacent vertices u,vu,v, and let Hn,x,y1,2H^{1,2}_{n,x,y} be the construction defined in the source for parameters x,yx,y. Extremal perfect-matching conjecture. There exists n0Nn_0\in\mathbb{N} such that, for every 3-graph HH of order nn0n\ge n_0 without isolated vertices, if

σ2(H)>max{σ2(Hn,x,y1,2):0x,yn31, x+yn31},\sigma_2(H)>\max\left\{\sigma_2(H^{1,2}_{n,x,y}):0\le x,y\le\frac n3-1,\ x+y\le\frac n3-1\right\},

then HH contains no perfect matching if and only if HH is a subgraph of Hn,n/32H_{n,n/3}^2. The source explains that an earlier conjecture fails when s=n/3s=n/3 and near that range, motivating this strengthened extremal formulation; its resolution is not supplied.

Sources & referencesView supporting material

Primary source

Yan Wang and Yi Zhang, “Vertex degree sums for perfect matchings in 3-uniform hypergraphs”, arXiv:2401.03713 (2024).

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