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Coloring distance graphs on the plane. (English) Zbl 1514.05057

Summary: We consider the coloring of certain distance graphs on the Euclidean plane. Namely, we ask for the minimal number of colors needed to color all points of the plane in such a way that pairs of points at distance in the interval \([1, b]\) get different colors. The classic Hadwiger-Nelson problem is a special case of this question – obtained by taking \(b = 1\). The main results of the paper are improved lower and upper bounds on the number of colors for some values of \(b\). In particular, we determine the minimal number of colors for two ranges of values of \(b\) – one of which is enlarging an interval presented by G. Exoo [Discrete Comput. Geom. 33, No. 1, 117–123 (2005; Zbl 1055.05048)] and the second is completely new. Up to our knowledge, these are the only known families of distance graphs on \(\mathbb{R}^2\) with a determined nontrivial finite chromatic number. Moreover, we present the first 8-coloring for \(b\) larger than values of \(b\) for the known 7-colorings. As a byproduct, we give some bounds and exact values for bounded parts of the plane, specifically by coloring certain annuli.

MSC:

05C15 Coloring of graphs and hypergraphs
05C12 Distance in graphs
05C10 Planar graphs; geometric and topological aspects of graph theory

Citations:

Zbl 1055.05048

References:

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