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**Sudoku, Quadruples** - Standard 9x9 sudoku: The digits 1 through 9 appear in every row, column, and box without repetition. - Quadruples: Digits in a quadruples circle must appear at least once in the four cells surrounding the circle. For more of our puzzles, please visit https://missingdeck.net or join our mailing list to get a weekly digest of puzzles: missingdeck.net/mailing