Two sets of N cells with N+1 candidates each, linked by a Restricted Common Candidate; their other common candidate is eliminated from all cells seeing both ALS.
An ALS is N cells with N+1 candidates. Two ALSs are linked by a Restricted Common Candidate (RCC) — a digit that can only go in one of the two ALSs. This means any other candidate shared by both ALSs can be eliminated from cells seeing both.
Extremely powerful; generalizes Naked Pairs, XY-Wings, and many other techniques.
258 | 258 | 1 | 4 | 7 | 9 | 8 | 6 | 3 |
| 4 | 6 | 7 | 2 | 9 | 8 | 5 | 7 | 1 |
| 3 | 9 | 58 | 37 | 6 | 4 | 1 | 8 | 35 |
2579 | 2579 | 2579 | 8 | 4 | 3 | 1 | 9 | 2 |
| 1 | 4 | 3 | 57 | 8 | 25 | 6 | 7 | 9 |
| 2 | 3 | 6 | 9 | 35 | 1 | 7 | 4 | 35 |
| 9 | 6 | 8 | 35 | 2 | 9 | 3 | 5 | 4 |
| 8 | 5 | 2 | 6 | 4 | 3 | 2 | 1 | 7 |
| 7 | 9 | 35 | 2 | 5 | 6 | 8 | 3 | 4 |
ALS-A: R1C1,R1C2 → {2,5,8}. ALS-B: R4C1,R4C2,R4C3 → {2,5,7,9}. RCC=2 → Eliminate 5 from cells seeing all 5s in both ALS.
This 9×9 puzzle is solver-verified to require this technique on its solution path.