ALS-XZ
Two almost-locked sets linked by a restricted candidate lock a digit.
Learn the ALS-XZ Sudoku technique: two almost-locked sets sharing a restricted common candidate lock a shared digit, cut from any cell that sees every copy.
How to use it
- Find two almost-locked sets. An almost-locked set is a group of cells in one unit with exactly one more candidate than cells. Find two of them that share two candidates, X and Z.
- Check the restricted common X. X must be restricted: every cell holding X across both sets must see the others, so X can land in at most one of the two sets.
- Lock and eliminate Z. The set that misses X collapses to a locked set and must place Z, so Z is trapped in the two sets — remove Z from any outside cell that sees every Z in both sets.