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arXiv · 1905.07913

Variations on the Petersen colouring conjecture

François Pirot·Jean-Sébastien Sereni·Riste Škrekovski
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Abstract

The Petersen colouring conjecture states that every bridgeless cubic graph admits an edge-colouring with $5$ colours such that for every edge $e$, the set of colours assigned to the edges adjacent to $e$ has cardinality either $2$ or $4$, but not $3$. We prove that every bridgeless cubic graph $G$ admits an edge-colouring with $4$ colours such that at most $\frac45\cdot|V(G)|$ edges do not satisfy the above condition. This bound is tight and the Petersen graph is the only connected graph for which the bound cannot be decreased. We obtain such a $4$-edge-colouring by using a carefully chosen subset of edges of a perfect matching, and the analysis relies on a simple discharging procedure with essentially no reductions and very few rules.

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François Pirot, Jean-Sébastien Sereni, Riste Škrekovski. 2019-05-20. Variations on the Petersen colouring conjecture. https://doi.org/10.37236/8515

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