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Meaning of four-color problem

four'-col'or prob"lem

Pronunciation: (fôr'kul'ur, fōr'-), [key]
— Math. Math.
  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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.