Practice
Scanning a diagonal
A diagonal works like a row: it holds 1 to 9 once. So scan it like one.
Next
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
5
9
1
6
7
2
8
9
3
Digits
Corner
Centre
Colour
Digits
ABC
1
2
3
4
5
6
7
8
9
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