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