8
3
9
5
4
5
8
7
3
9
5
6
2
4
8
2
2
3
5
6
1
5
4
9
5
6
3
7
2
8
3
7
"Chess demands total concentration." — Bobby Fischer
"Chess demands total concentration." — Bobby Fischer
When a box has only two empty cells, you know exactly which two digits fill them.
When a box has only two empty cells, you know exactly which two digits fill them.