X-Chain / XY-Chain
Extreme
Used by Smart Hint
A longer alternating chain of links that traces a digit (or a sequence of digit pairs) across the board to find a single elimination.
- First colour in the chain
- Second colour in the chain
- Where the conclusion lands
- Candidate ruled out
How it works
- Digit 6 traces a chain of alternating strong links: A1 ↔ G1 (row 1's only two 6s), G1 ↔ G6 (column G's only two 6s), G6 ↔ C6 (row 6's only two 6s) — colored teal/red/teal/red as it goes.
- The two ends of the chain, A1 (teal) and C6 (red), are opposite colors, so at least one of them is 6. C1 sees both — it's eliminated.
- This is a simplified four-cell example; real X-Chains and XY-Chains can run much longer before closing the loop.