Exact-value conjecture for Ryser's function

For integers rr and tt with 2tr2\leq t\leq r, let an (r,t)(r,t)-graph be an rr-uniform, rr-partite, tt-intersecting hypergraph, and define

Ryser(r,t)=max{τ(H):H is an (r,t)-graph},\operatorname{Ryser}(r,t)=\max\{\tau(\mathcal H):\mathcal H\text{ is an }(r,t)\text{-graph}\},

where τ(H)\tau(\mathcal H) is the cover number. Bustamante--Stein and Király--Tóthmérész's exact-value conjecture. For all 2tr2\leq t\leq r,

Ryser(r,t)=rt2+1.\operatorname{Ryser}(r,t)=\left\lfloor\frac{r-t}{2}\right\rfloor+1.

The paper proves this value in the range r3t1r\leq 3t-1 and establishes further partial results, but the formula remains conjectural in general.

Sources & referencesView supporting material

Primary source

Anurag Bishnoi, Shagnik Das, Patrick Morris and Tibor Szabó, “Ryser's Conjecture for t-intersecting hypergraphs”, arXiv:2001.04132 (2020).

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