Math 2.0

Combinatorics Definition

Graph colouring

Definition

Let GG be a graph with vertex set VV, and let CC be a set, the set of colours. A colouring of GG with colours in CC is a function c:V→Cc : V \to C such that c(u)≠c(v)c(u) \neq c(v) for any two adjacent vertices uu and vv.

Remarks

Such a colouring is also called proper. A colouring with a set of kk colours is a kk-colouring. Each colour class c−1(x)c^{-1}(x) is an independent set. A graph has a 22-colouring if and only if it is bipartite. The subject started with the colouring of maps. Francis Guthrie stated the four colour conjecture in 1852.

Where this leads

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Further reading

  1. Web https://en.wikipedia.org/wiki/Graph_coloring, Definition and terminology
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