The numerals in Sudoku puzzles are used for convenience; arithmetic relationships between numerals are irrelevant. Any set of distinct symbols will do, such as letters, shapes, or colours. In fact, ESPN published Sudoku puzzles substituting the positions on a baseball field for the numbers 1 through 9, while Viz magazine has published a Doctor Who version of the game, using images of the television series’ first nine leading actors in place of the numerals. Dell Magazines, the puzzle’s originator, has been using numerals for Number Place in its magazines since they first published it in 1979.
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