They say it's the Rubik's Cube® of the 21st century! Be honest: you were never truly convinced that we needed a Rubik's Cube of the 20th century. But who would have predicted that one of the main reasons for people buying newspapers worldwide in 2005 was going to be a funny little number puzzle invented in New York in the '70s? Here in the US, we've actually been a little slow on the uptake, and the New York Times notably hasn't (yet) deigned to join the party started this summer by the New York Post, and gatecrashed by the Washington Post, the Los Angeles Times, et al. But in the UK, for instance, Sudoku has officially become a phenomenon. (That's mediaspeak for "fad that nobody was expecting but, hey, we're going with it, even if we're the Guardian.") The excellent Wikipedia entry tells the whole tale. Six books on Sudoku, either books of puzzles or guides to solving, are already cataloged in WorldCat. Such works should be classed at 793.73 Puzzles and puzzle games, under 793.7, the number for indoor games and amusements "not characterized by action" -- a description at which some aficionados might conceivably take umbrage? Crossword puzzles go at 793.732, and other word games at 793.734; mathematical games and recreations are classed at 793.74. We at Dewey Manor don't think Sudoku really counts as a mathematical game, since it doesn't require players to carry out any mathematical operations. Sure, in most Sudoku puzzles, the symbols that are used to fill in the grid happen to be numerals; but variants exist, such as the Guardian's Godoku, that use letters rather than numerals, and the operations involved are logical rather than mathematical.