X-Chain
Expert
A chain of alternating strong and weak links on a single letter. Following the chain from end to end shows that one of the two endpoints must hold the letter, so it is ruled out of any cell that sees both ends.
Expert
A chain of alternating strong and weak links on a single letter. Following the chain from end to end shows that one of the two endpoints must hold the letter, so it is ruled out of any cell that sees both ends.