PlaySudoku.us
Medium · Puzzle #284
1
9
7
3
4
8
4
5
9
1
5
2
4
1
9
9
4
1
5
8
6
1
8
4
5
6
9
7
4
5
6
1
7
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.
If pointing pairs aren't visible, try box-line reduction. They're inverses — if one fails, try the other.
If pointing pairs aren't visible, try box-line reduction. They're inverses — if one fails, try the other.