ALS-XZ

ALS-XZ is the simplest ALS chain technique. Two Almost Locked Sets share a restricted common candidate (X), allowing elimination of any other common candidate (Z) from cells seeing all Z's in both sets.

Technique

1. Find two ALS (groups of N cells with N+1 candidates).
2. Find a restricted common candidate X (all X's in ALS1 see all X's in ALS2).
3. Find another common candidate Z that appears in both ALS.
4. Eliminate Z from cells that see all Z's in both ALS.

Tips

• The restricted common X can only be true in one ALS.
• This forces Z to be locked in at least one ALS.
• Any cell seeing all Z's in both sets can never be Z.