# Around the Petersen Colouring Conjecture

#### Wed, Feb 19, 2020 12:30 CET

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**Speakers:**
Jean-Sébastien Sereni

A number of old conjectures related to edge-colourings of 3-regular graphs remain vastly open. Among them, the Petersen colouring conjecture is a very strong statement, which implies most of these, such as the Berge—Fulkerson conjecture, and the 5-Cycle-double-cover conjecture. It 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. I will also discuss a variation of this conjecture using only 4 colours instead of 5, and show that all but at most 8/15·|E(G)| edges can be made to satisfy the above condition. Further, the bound is tight, and attained only by the Petersen graph. Various open questions on related topics will be presented too.

The talk is based on a joint work with François Pirot & Riste Škrekovski.