In the summer of 1872, the mathematicians Georg Cantor and Richard Dedekind both spent their holiday in the scenic lakefront village of Gersau, Switzerland, where they crossed paths for the first time and took a long walk together to discuss their ideas. To any spectator, the two men strolling along the lakeshore would have seemed an odd match. At 27, Cantor was tall, broad-shouldered, and boisterous. He reveled in attention from his peers, but beneath it all, he was deeply anxious about how the