Tuesday, 14 February 2017 | Paul Stephenson
Most Sudoku puzzles use the numbers 1 to 9, but you can use anything – letters, colours, shapes, …And you can make up puzzles with fewer items. We shall use just 4. If you think such puzzles are likely to be too simple, I warn you that we shall move from 'single' Sudoku to 'double' Sudoku and even 'triple double' Sudoku.
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