Techniques / Almost Locked Sets
ALS-XY-Wing
Three almost locked sets: C is linked to A and to B by two different restricted commons.
Take three almost locked sets A, B and C. C is linked to A by a restricted common digit X and to B by a different restricted common digit Y. A and B share a third digit Z.
If X is not in A, then A holds Z. If X is in A, then C loses X and holds Y, so B loses Y and holds Z. So one of A and B contains Z. Any cell that sees all Z candidates of both A and B cannot be Z.
Notation
Almost Locked Set XY-Wing: 9 can be removed from r7c4.
pattern removed
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