论文标题

Ryser的猜想$ t $ - 更新超图

Ryser's Conjecture for $t$-intersecting hypergraphs

论文作者

Bishnoi, Anurag, Das, Shagnik, Morris, Patrick, Szabó, Tibor

论文摘要

一个众所周知的猜想,通常归因于Ryser,指出$ r $ $ r $ r $ r $统一的超盖的封面数量最多为$ r-1 $ 1 $倍。尽管付出了巨大的努力,尤其是在相交的情况下,这种猜想仍然敞开着,激发了对原始猜想的变体的追求。最近,Bustamante和Stein以及Király和TóthMérész认为,在假设HyperGraph为$ t $ interce的假设上,封面数字$τ(\ Mathcal {h})$ thypraph $ \ nathcal $ \ nathcal \ nathcal {h} $最多是$ r -r -r -r -r -r -r -t -t $。在这些论文中,事实证明,对于$ r \ leq 4t-1 $,猜想是正确的,但也不必尖锐。当$ r = 5 $和$ t = 2 $时,一个人具有$τ(\ Mathcal {h})\ leq 2 $。 我们将这些结果扩展到两个方向。首先,对于所有$ t \ geq 2 $和$ r \ leq 3t -1 $,我们证明了这些超图的盖子上的紧密上限,这表明它们实际上满足$τ(\ nathcal {h})\ leq \ leq \ leq \ lfloor(r -t -t)/2 \ rfloor + 1 $ + 1 $。其次,我们扩展了已知猜想为真实的$ t $范围,表明它适用于所有$ r \ leq \ frac {36} {7} {7} t-5 $。我们还介绍了有关此主题的几种相关变体。由于我们的紧密界限,我们解决了$ k $ - $ t $ tum-disterting Hypergraphs的问题,所有$ k \ geq 3 $和$ t \ geq 1 $。我们进一步给出了严格的$ t $更换超图和$ s $ cover $ t $ thum-termectery超图的封面数量的界限。

A well-known conjecture, often attributed to Ryser, states that the cover number of an $r$-partite $r$-uniform hypergraph is at most $r - 1$ times larger than its matching number. Despite considerable effort, particularly in the intersecting case, this conjecture remains wide open, motivating the pursuit of variants of the original conjecture. Recently, Bustamante and Stein and, independently, Király and Tóthmérész considered the problem under the assumption that the hypergraph is $t$-intersecting, conjecturing that the cover number $τ(\mathcal{H})$ of such a hypergraph $\mathcal{H}$ is at most $r - t$. In these papers, it was proven that the conjecture is true for $r \leq 4t-1$, but also that it need not be sharp; when $r = 5$ and $t = 2$, one has $τ(\mathcal{H}) \leq 2$. We extend these results in two directions. First, for all $t \geq 2$ and $r \leq 3t-1$, we prove a tight upper bound on the cover number of these hypergraphs, showing that they in fact satisfy $τ(\mathcal{H}) \leq \lfloor(r - t)/2 \rfloor + 1$. Second, we extend the range of $t$ for which the conjecture is known to be true, showing that it holds for all $r \leq \frac{36}{7}t-5$. We also introduce several related variations on this theme. As a consequence of our tight bounds, we resolve the problem for $k$-wise $t$-intersecting hypergraphs, for all $k \geq 3$ and $t \geq 1$. We further give bounds on the cover numbers of strictly $t$-intersecting hypergraphs and the $s$-cover numbers of $t$-intersecting hypergraphs.

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