Euler’s 243-Year-Old ‘Impossible’ Puzzle Gets a Quantum Solution

In 1779, the Swiss mathematician Leonhard Euler posed a puzzle that has since become famous: Six army regiments each have six officers of six different ranks. Can the 36 officers be arranged in a 6-by-6 square so that no row or column repeats a rank or regiment? The puzzle is easily solved when there are five ranks and five regiments, or seven ranks and seven regiments. But after searching in vain…

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