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