Aligned Pair Exclusion
Extreme
Reference only
Two cells that don't share a unit are checked against every "almost locked" set nearby — any combination of their candidates that would leave one of those sets with no valid completion is ruled out.
The solver does not attempt this technique, so Smart Hint will never suggest it. It is documented because you may still want to spot it yourself.
- Cells that establish the pattern
- Where the conclusion lands
- Candidate ruled out
How it works
- A1 and D1 don't share a row, column, or box, but B2 and C3 form an Almost Locked Set on {2, 3} that both A1 and D1 can see.
- Pairing A1 = 5 with D1 = 5 leaves the {2,3} pair with no legal way to fill B2/C3 alongside it — so that combination is excluded, ruling out 5 at A1 specifically.