4
2
9
8
7
6
8
4
3
5
2
9
7
6
8
3
5
1
7
1
8
2
5
7
9
6
5
6
4
9
3
1
4
9
3
"A person who never made a mistake never tried anything new." — Albert Einstein
"A person who never made a mistake never tried anything new." — Albert Einstein
Set theory provides the formal foundation for Sudoku's rules: each digit must appear exactly once per set.
Set theory provides the formal foundation for Sudoku's rules: each digit must appear exactly once per set.