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Erdős problem 508

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This upper bound for the chromatic number of the plane was observed by John R. Isbell. His approach was dividing the plane into hexagons of uniform size and coloring them with a repeating pattern. A proof can probably be found in:

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The source's own material, retained exactly.

5 retained statements36c6d0fef71a

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FormalConjectures/ErdosProblems/

508.lean

Retained formal statement5 of 5

The Hadwiger–Nelson problem asks: How many colors are required to color the plane such that no two points at distance 1 from each other have the same color?

FormalConjectures/ErdosProblems/508.leanErdos508.HadwigerNelsonProblem1 lineExact file
(SimpleGraph.UnitDistancePlaneGraph Set.univ).chromaticNumber = sorry
OpenStatement only, no proof