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Or phrased differently, are non-symmetrical Sudoku puzzles considered legal?

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    $\begingroup$ "Considered" by whom? Most published Sudoku are symmetric. Similarly, almost all crosswords have a symmetric diagram. In both cases there are violations, usually because there is some good reason, such as making a minimum clue Sudoku or a crossword theme that makes an asymmetric diagram make sense. I have not noticed either contributing to the fun of solving the puzzle. They are certainly tradition. $\endgroup$ – Ross Millikan May 20 '14 at 3:38
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Any sudoku puzzle with enough numbers filled in that the solution is unique is considered a "valid" or "legal" sudoku. Before some time in 2005, the Toronto Metro newspaper published sudoku puzzles (although not named Sudoku at the time) where exactly four numbers in each row, column, and 3x3 square were filled in, and those were never rotationally symmetrical.


However, the sudokus that newspapers tend to publish usually have some form of symmetry, usually for aesthetic reasons. Usually this symmetry is rotational.

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Yes, non-symmetric Sudoku puzzles are valid. For example:

enter image description here

This is a minimal Sudoku puzzle, with exactly 17 clues, and is not symmetric.

Image courtesy of the Wikimedia Commons.

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