Take an outline map of the lower 48 U.S. states and four crayons. Can you shade in the map so that every state is a different color than each of its neighbors, without resorting to a fifth color? This ...
Allow me to introduce you to what was, for over 100 years, the Four Color Conjecture—that is, until the mid '70s, when mathematicians Appel and Haken made it the first major mathematical concept to be ...
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