Sudoku, which is Japanese for ‘pointless’, is a form of torture invented by sadistic Orientals to punish those with too much time on their hands. The ubiquitous grids now appear on cereal packets, knitting patterns, flat pack furniture instructions, socks and railway timetables, though they can be a valuable teaching aid, since piles of Sudoku books can be bound together and used to hit lethargic pupils around the head.