Four Is Not Enough

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Patrick Honner
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How many colors do you need to color an infinite plane so that no points 1 unit apart are the same color?

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Greg Egan 5mos

[6/6] So no same-coloured points can be exactly a distance of 1 apart. Here’s a great intro by @MrHonner to the “Hadwiger-Nelson problem”: how many colours are needed to ensure that no two points on the plane a unit distance apart share the same colour?