Every finite planar graph has chromatic number at most four. This stronger theorem is distinct from the elementary five colour theorem; the latter's Kempe chain proof does not prove this assertion.
The Four Color Theorem is a famous result in mathematics and graph theory stating that, given any arrangement of regions on a plane (such as a map), four colors are sufficient to color the regions such that no two adjacent regions share the same color. Adjacent regions are those that share a common boundary, not just a point. The theorem was first proposed in 1852 by Francis Guthrie and was proven in 1976 by Kenneth Appel and Wolfgang Haken.
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