ALS Chain
Chain almost locked sets and use the shared candidates at their ends to derive eliminations.
All candidates have been entered in the empty cells.
A and B mark the two ends of the chain. Assume every candidate in A is false. On a solid link, one false end makes the other end true. On a dashed link, one true end makes the other end false. Apply these rules from A to B in link order. Under this assumption, B is true. Including the case where A is true, at least one of A and B is true. Candidate 9 marked × can be removed.