Region Forcing Chains
Try each place a digit could go in a row, column or box, follow the chain from each, and keep only what every branch agrees on.
How it works on this board
Every possible placement of 8 in the target house forces 8 into one common cell
3
2
9
4
6
1
7
6
5
3
8
6
3
2
5
3
8
6
3
4
3
8
7
2
7
2
1
8
2
9
7
3
6
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