X-Chain
When one digit travels through alternating strong and weak links.
Explanation
An X-Chain follows one candidate digit through alternating strong and weak links. If the chain starts and ends with strong links, one endpoint must contain that digit, so cells seeing both endpoints can remove it.
Practice tip
Scan one candidate at a time. Longer X-Chains are useful after the shorter Turbot Fish patterns no longer apply.
Example steps
- Pick one candidate digit.
- Trace strong, weak, strong links in alternation.
- Remove the digit from cells that see both strong-link endpoints.