Alignment

**Sudoku, Column Indexing, Quadruples** - Standard 9x9 sudoku: The digits 1 through 9 appear in every row, column, and box without repetition. Column Indexing: Digits placed in red cells (columns 1, 5, 9) indicate the position of the corresponding column number in that row. For example, if r2c5 is a 3, then the 5 in row 2 appears in column 3. - 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