Article
Keywords:
vertex colouring; infinity graph; decomposition of the real plane
Summary:
What is the least number of colours which can be used to colour all points of the real Euclidean plane so that no two points which are unit distance apart have the same colour? This well known problem, open more than 25 years is studied in the paper. Some partial results and open subproblems are presented.
References:
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Zbl 0418.05026