Hidden Unique Rectangle
Three corners hold only the two digits, and a strong link runs into the fourth. One of the digits goes from that corner.
How it works on this board
A strong link on 6 into the fourth corner makes the pattern swappable if 5 is true
9
6
2
4
7
2
4
6
4
1
6
3
2
9
5
2
3
9
9
1
4
7
3
9
8
6
1
5
8
9
8
4
6
9
2
3
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