7
8
6
1
4
8
7
1
6
4
2
7
5
3
1
6
9
8
9
4
1
5
6
6
8
3
8
5
7
6
5
1
9
3
4
2
"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.