nLab four-colour theorem

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Idea

The four-colour theorem, or four colour map theorem, states that given any separation of a plane into contiguous regions, called a map, the regions can be coloured using at most four colours so that no two adjacent regions have the same colour. Regions are considered adjacent if they share a boundary segment.

References

See also

On the logical equivalence between the four-colour theorem and a statement about the transition from the small N limit to the large N limit for Lie algebra weight systems on Jacobi diagrams via the 't Hooft double line construction:

On a reformulation of the four-colour theorem as a statement about typing in lambda calculus:

Fawcett showed that the four-color theorem is equivalent to the existence of a left adjoint (that is, preserving epimorphisms) from planar graphs to Set:

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