The Heawood map coloring conjecture [by] J. W. T. Youngs.

The Heawood map coloring conjecture [by] J. W. T. Youngs.

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The four-color conjecture for a sphere is a famous unsolved problem, and the only information available today is that the chromatic number of a sphere is either four or five. On the other hand, it has been known for three-quarters of a century that t...