When you begin a new sudoku, some of the squares will have numbers already in them, and have a gray background. The easier the sudoku, the more squares like this you will have. These squares cannot be altered
The rules of Sudoku are simple, fill all empty squares so that the numbers 1 to 9 appear once in:
- each of the nine columns,
- each of the nine rows, and
- each of the nine boxes.
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