Defined But Irregular Quads
by myShoggoth
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Normal sudoku rules apply. Digits inside the circles must appear in the surrounding cells. Digit in columns 1, 5, and 9 indicate the column where the 1 5, and 9 respectively can be found in its row - a 3 in column 1 means the 1 for that row is in its column 3. Regions are irregular.