four-color problem

American  

[fawr-kuhl-er, fohr-] / ˈfɔrˈkʌl ər, ˈfoʊr- /

noun

Mathematics.

1. the problem, solved in 1976, of proving the theorem that any geographic map can be colored using only four colors so that no connected countries with a common boundary are colored the same color.

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Etymology

Origin of four-color problem

First recorded in 1875–80