Harris's conjecture on the Hall ratio and fractional chromatic number
Harris's conjecture on the Hall ratio and fractional chromatic number
Let be a graph, let denote its fractional chromatic number, and let denote its Hall ratio, the maximum of over all non-null subgraphs . Harris's Hall-ratio conjecture. There exists a constant such that
for every graph . The conjecture proposed a universal constant-factor upper bound on the fractional chromatic number in terms of the Hall ratio, but the paper's constructions refute it by producing graphs for which the ratio is unbounded.
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Primary source
Adam Blumenthal, Bernard Lidicky, Ryan R. Martin, Sergey Norin, Florian Pfender and Jan Volec, “Counterexamples to a conjecture of Harris on Hall ratio”, arXiv:1811.11116 (2020).
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