A weaker stable-set colorability conjecture for set systems

Let r2r\geq 2 and let F\mathcal{F} be a set system. Write Frstab~\mathcal{F}_{\widetilde{r-\operatorname{stab}}} for the family obtained by retaining the source's weakened notion of rr-stability, let KGr(Frstab~)\operatorname{KG}^r(\mathcal{F}_{\widetilde{r-\operatorname{stab}}}) be the associated rr-uniform Kneser hypergraph, let χ\chi denote its chromatic number, and let cdr(F)cd_r(\mathcal{F}) denote the rr-colorability defect of F\mathcal{F}. The weaker conjecture. For every such rr and F\mathcal{F},

χ(KGr(Frstab~))cdr(F)r1.\chi\left(\operatorname{KG}^r\left(\mathcal{F}_{\widetilde{r-\operatorname{stab}}}\right)\right)\geq\left\lceil\frac{cd_r(\mathcal{F})}{r-1}\right\rceil.

The paper proposes this as a weaker version of the conjecture it disproves, but does not establish it; its status is therefore open.

Sources & referencesView supporting material

Primary source

Hamid Reza Daneshpajouh, “A counterexample to a conjecture on the chromatic number of r-stable Kneser hypergraphs”, arXiv:2203.03019 (2022).

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