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Jonathan Davidson
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Spindle-free unit distance graph is not 3-colorable.
Case 1 of 6
Pentagon: 5 → 6 → 9 → 14 → 20 → 5
Spindle-free unit distance graph is not 3-colorable.
Vertices show their number and their assigned color. Gray vertices have not yet been colored. Each deduction highlights a vertex and the two neighbors forcing its color. Every case ends with a highlighted edge whose endpoints have the same color.
Enable JavaScript to watch the six cases of the coloring proof.