MHB The Chromatic Number of the Plane is at Least 5

[Ackbach]

I love this stuff! An amateur gets this one, though his result is refined by the pros. His paper on arXiv is here.

 

[topsquark]

I love this stuff! An amateur gets this one, though his result is refined by the pros. His paper on arXiv is here.

Okay, why isn't the number four? Is this diagram of his not flat in the plane? I messed around with the 4 color theorem as a kid and I heard it was proved at some point. How is this one different?

-Dan

 

[I like Serena]

Okay, why isn't the number four? Is this diagram of his not flat in the plane? I messed around with the 4 color theorem as a kid and I heard it was proved at some point. How is this one different?

-Dan

The 4-color theorem is for coherent neighboring countries.
This is a more general theorem for graphs for which apparently 4 colors is not enough. We need at least 5 colors.