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Peter Kronheimer: Max Dehn and the Dehn Twist

Open Neighborhood seminar Wednesday, Feb. 19 at 4:30 PM in SC507. Snacks to follow in the Common Room. Our speaker is Peter Kronheimer:
Title: Max Dehn and the Dehn Twist:
Abstract: Max Dehn made many remarkable contributions to mathematics, and his name pops up in lots of places, most often in topology, where we have "Dehn surgery", the "Dehn twist", and "Dehn's lemma". Famously, Dehn supplied an incorrect proof of the lemma that bears his name. The mistake wasn't noticed for nearly a decade, and took nearly another four decades to fix. In this talk, I won't mention the lemma, but I will say a few words about Dehn himself, a few more about his early work on "scissors congruences", and then yet more on the Dehn twist, closing with a recent result about Dehn twists in four dimensions.