Practise: ALS-XY-Wing
This verified teaching position begins directly with a real ALS-XY-Wing pattern. Follow the chain, inspect the candidates and make the deduction before you continue.
You are at the verified key position. Use a hint to follow the chain link by link when you need support.
Your turn first
Spot the idea before the hint explains it
- 1. Look
- 2. Check
- 3. Proof
Look at the marked starting cells and their candidates. Which digit or candidate relation is forced, and what visible row, column or box fact supports your idea?
How to spot it
First find small ALS with two to four cells. Keep only links where each occurrence of the shared digit in one set sees every occurrence in the other: that digit is a restricted common candidate. Build two such links through one middle ALS, using different digits X and Y. Finally check an outside candidate Z that sees all Z positions in both outer ALS.
Put it to use
Where you will meet it
Expert grids are the only place this pattern regularly decides the solve. Bring your notes.
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