Unique Rectangle Type 4
One side has a strong link in one rectangle digit. Keeping the other digit in either linked cell would leave two solutions, so it goes from both.
How it works on this board
7 forms a strong link along one side, and keeping 6 would leave two solutions
8
6
3
1
2
2
4
5
9
6
3
4
5
8
1
5
2
3
9
4
2
7
1
4
8
3
5
4
8
5
1
7
9
7
5
4
6
1
3
1
3
9
5
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