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