8
5
7
1
3
7
7
5
1
8
3
3
1
8
2
8
3
5
1
8
6
3
7
3
1
2
3
8
1
2
9
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.