In 2002, a Russian mathematician named Grigori Perelman solved the Poincaré conjecture, a problem that had resisted proof for a century. But soon after he gave up mathematics and retreated to his mother's apartment in St. Petersburg. Why did Perelman turn his back on the world? This question haunts Masha Gessen’s “Perfect Rigor,” a dogged portrait of an elusive man... [text]