ALS-Chain

Link almost locked sets in a row, each pair connected by a restricted common digit, and consecutive links using different digits. At the two ends of the chain, look for a digit Z that both end sets contain and that is not used in the links.

If the first set does not contain Z, the chain forces the last set to hold it. So at least one end set contains Z, and every cell that sees all Z candidates of both ends cannot be Z. ALS-XZ and ALS-XY-Wing are the chains of two and three sets.

Notation

Almost Locked Set Chain: 5 can be removed from r3c9. chain: 8 in r3c4 → 8 in r3c6. chain: 9 in r3c6 → 9 in r4c6. chain: 8 in r4c6 → 8 in r4c3.