Four color theorem

Planar maps require at most four colors

In mathematics, the four color theorem, or the four-color map theorem, states that no more than four colors are required to color the regions of any map so that no two adjacent regions have the same color. Adjacent means that two regions share a common boundary of non-zero length (i.e., not merely a corner where three or more regions meet). It was the first major theorem to be proved by use of a computer.

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