Techniques / Almost Locked Sets
ALS-XZ
Two almost locked sets linked by a restricted common digit.
An Almost Locked Set (ALS) is N cells in one unit with N+1 candidates in total. If you remove one candidate, the rest becomes locked. Take two ALSs, A and B, with a restricted common digit X (every X in A sees every X in B) and a second common digit Z.
If X is in A, then X is not in B, and B loses X, so B holds Z. If X is not in A, then A holds Z. Either way one of the two sets holds Z, so Z can be removed from every cell that sees all Z candidates in both sets.
Notation
Almost Locked Set XZ-Rule: 5 can be removed from r2c9.
pattern removed
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