X-Chain

X-Chain is a single-digit chain technique that connects cells through alternating strong and weak links. When both endpoints are on strong links, the digit can be eliminated from cells that see both endpoints.

Technique

1. Choose a digit and find strong links (conjugate pairs in a house).
2. Build a chain alternating between strong links and weak links (cells sharing a house).
3. The chain must start and end with strong links.
4. Eliminate the digit from cells that see both chain endpoints.

Tips

• X-Chains generalize Skyscrapers and Two-String Kites to longer chains.
• Odd-length chains (3, 5, 7 cells) are the ones that produce eliminations.
• Either endpoint must contain the digit, so any cell seeing both can't have it.