ALS-XZ
Two Almost Locked Sets joined by a restricted common candidate force another shared candidate into one set or the other, eliminating it from cells that see all of its holders.
How it works
- 1A1 + A2 hold {1, 3, 4} across two cells of column A — three digits for two cells, so they are one candidate short of locking: an Almost Locked Set.
- 2D1 + E1 do the same with {3, 4, 5} in row 1. Digit 3 lives in exactly one cell of each set, A1 and D1, and those two share row 1 — a restricted common, so at most one set can actually use it.
- 3Whichever set goes without the 3 has as many digits left as cells and locks, and 4 is one of the digits it must then place. So the 4 lands in A1/A2 or in D1/E1.
- 4B1 sees every one of those cells — A1, D1 and E1 along row 1, A2 through the box — so its own 4 can go.
- First colour in the chain
- Cells that establish the pattern
- Where the conclusion lands
- Candidate ruled out