Rules

1. Irregular sudoku rules apply: Place the digits 1-9 once each in every row, column and 9-cell region (regions are divided by thick black borders).

2. For pairs of digits in cells separated by a white dot, one must be 1 greater than the other.

3. For pairs of digits in cells separated by a black dot, one must be double the other.

4. Digits in large white circles must appear at least once in the four surrounding cells.