A controversy erupted in St. Louis last week when Magnus Carlsen, the world chess champion, withdrew from a top tournament. One interpretation of his decision, drawing upon his tweet, is that he believes competitor Hans Niemann, who beat him in the third round, may have been cheating with computer assistance. Suspicions were raised further when Niemann admitted having cheated twice previously, and when Chess.com issued a statement alleging yet further cheating and banning Niemann from its site.