What Is the Langlands Program?

Not long ago, I was asked to explain the so-called Langlands program in a single tweet. Impossible, I immediately thought. It’s one of the biggest, most sweeping projects in mathematics, capable of connecting distant realms of research and, naturally, fiendishly difficult to describe. But then I remembered the story of a student asking the great Talmudic sage Hillel to explain the whole Bible…

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