Oxford Fog

- Standard sudoku rules apply: The digits 1 through 9 appear in every row, column, and box. - Fog: Part of the grid is covered with fog. As correct digits are placed, the fog will clear from cells surrounding the correct digit, revealing additional clues. Digits can be placed within the fog. - Quadruples: Digits in a Quadruple circle must be placed at least once in the four cells touching that circle.