Example 4.4.1.

Find the chromatic number of the graphs below.

A copy of K6: six vertices arranged in a hexagon, with every vertex adjacent to every other vertex.
Six vertices arranged in a triangle (with three vertices along each side). Six edges form the outside of the triangle, and three edges connect the center vertices of each side (in an upside-down triangle).
A copy of K2,3, with a row of two vertices on a top row, each adjacent to each of three vertices on a bottom row
Solution.
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