Map Colouring with Polydron
14 February 2017
The 4 Colour Map Theorem says that you never need more than 4 colours to colour a map so that regions with the same colour don’t touch. You have to count the region round the edge because the theorem is really about a map drawn on a sphere. The theorem is shape-blind. It doesn’t matter what shape a region is. What matters are the regions it shares a border with.
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