four-color problem

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

noun Mathematics.

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.

Origin of four-color problem

First recorded in 1875–80
Also called four-color theorem. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019