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Consecutive Quads Sudoku (628)
Instruction:
Apply Classic Sudoku rules.
Additionally, a white circle means that the 2×2 area around it contains exactly one consecutive pair of digits. A black circle means that the 2×2 area around it contains at least two consecutive pairs of digits. Repeats are allowed (e.g., 2-4-5-6 is valid with 4-5 and 5-6, and so is 2-5-6-5). (Not all possible circles are necessarily given.)