What is the minimum number of colours needed to colour the plane in such a way that any two points that are at distance 1 from each other always have different colours? This is known as the Hadwiger–Nelson problem, and it has been an open question in geometry since 1950. This minimum number of colours is known as the
It’s great you have opened up your archive of old posts! A very valuable resource.
Thanks, Roger. It was a good decision on the part of my publicity team!