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By Henry Kwok

Rules of Quadruple Clue Sudoku

This is a variation of sudoku on a "standard" 9x9 grid which contains a set of special clue-numbers. These are small numbers provided by sets of 4 small digits. Each set of 4 small digits in the intersection of two grid lines stands for the numbers in the four cells of the grid adjacent to this set.


Here is a brief explanation of how the special clue-numbers work. It can be seen that the 4 adjacent cells around each set of 4 small digits overlap one or more sets of adjacent cells with 4 small digits. For example, in the puzzle, taking the two sets of adjacent cells with small digits {4568} and {1789}, we find that they overlap at the cell with the number 8.
