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A three coloring of the vertex set for the Petersen graph (both pocket and across available).
In the field of graph theory, the Petersen graph is an undirected graph with 10 vertices and 15 edges. It is quite often a counterexample for many problems in graph theory.
The Petersen graph has a chromatic number of 3. What this means is that its vertices (the dots in the picture) can be colored using three colors (but not two) such that no edge (a line in the picture) connects two vertices (ie. dots) of the same color.