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arXiv · 1907.04066

Coloring count cones of planar graphs

Zdeněk Dvořák·Bernard Lidický
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Abstract

For a plane near-triangulation $G$ with the outer face bounded by a cycle $C$, let $n^\star_G$ denote the function that to each $4$-coloring $\psi$ of $C$ assigns the number of ways $\psi$ extends to a $4$-coloring of $G$. The block-count reducibility argument (which has been developed in connection with attempted proofs of the Four Color Theorem) is equivalent to the statement that the function $n^\star_G$ belongs to a certain cone in the space of all functions from $4$-colorings of $C$ to real numbers. We investigate the properties of this cone for $|C|=5$, formulate a conjecture strengthening the Four Color Theorem, and present evidence supporting this conjecture.

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Zdeněk Dvořák, Bernard Lidický. 2019-07-09. Coloring count cones of planar graphs. https://doi.org/10.1002/jgt.22767

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