Four-Color Theorem Is Still a Math Favorite

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In 1852, the mathematician Francis Guthrie was coloring in a map of English counties when he noticed that he needed only four colors. Was this always true, he wondered? The question captured the imagination of hobbyists and professionals alike — and in 1976, the mathematicians Kenneth Appel and Wolfgang Haken proved it, rather controversially using computers. Recently, mathematicians have revisited the four-color theorem and found a more efficient way to color maps with just four colors. On this episode of The Quanta Podcast, host Samir Patel speaks with writer Greg Barber about the “four-color disease,” its history of false starts and dashed hopes, and what modern mathematicians have…