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Easy · Puzzle #232
9
6
7
5
4
1
1
5
7
3
9
8
4
8
9
1
6
8
7
1
7
2
1
5
9
3
8
9
2
7
4
1
6
2
8
7
5
3
3
5
1
2
6
5
3
8
4
Scan by digit rather than by cell: find everywhere '7' must go before switching to '8'.
Scan by digit rather than by cell: find everywhere '7' must go before switching to '8'.
The hardest Sudoku puzzles require techniques equivalent to propositional logic — the same foundation used in computer proofs.
The hardest Sudoku puzzles require techniques equivalent to propositional logic — the same foundation used in computer proofs.