A note on two conjectures that strengthen the four colour theorem

Xuding Zhu

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arXiv · 1711.02848

A note on two conjectures that strengthen the four colour theorem

Xuding Zhu

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Abstract

There are two conjectures concerning planar graph colourings that are strengthenings of the four colour theorem. One concerns signed graph colouring and is proposed by M\'{a}\v{c}ajov\'{a}, Raspaud and \v{S}koviera. It asserts that every signed planar graph is $4$-colourable. Another concerns list colouring and is proposed by K\"{u}ndgen and Ramamurthi which asserts that if $L$ is a $2$-list assignment of a planar graph $G$, then there is an $L$-colouring of $G$ such that each colour class induces a bipartite graph. In this note we prove that the first conjecture implies the second one.

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Xuding Zhu. 2017-11-08. A note on two conjectures that strengthen the four colour theorem. https://arxiv.org/abs/1711.02848

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