VWXYZ-Ring
A VWXYZ-Ring is a double-linked ALS-XZ construction involving exactly five distinct cells and five distinct candidate digits across two almost locked sets. For non-overlapping sets, the cell-count split is 4+1 or 3+2. The sets share two different restricted common candidates, X and Y. These restrictions make both ALSs resolve into locked sets. Here, “Ring” refers to the double-linked ALS pair, not to an AIC ring.
What is a VWXYZ-Ring?
Each ALS consists of k unsolved cells in one house with exactly k+1 distinct candidate digits. Together, the two ALSs contain exactly five distinct cells and five distinct candidate digits. For non-overlapping sets, the possible cell-count splits are 4+1 or 3+2. They share two different restricted common candidates: for each of those digits, every occurrence in one ALS must see every occurrence in the other. A restricted common candidate may occur only once in an ALS; multiple occurrences are not required.
How to spot it
List ALS A and ALS B — five cells and five distinct digits in total — and verify two separate restricted commons. For an RCC elimination, check visibility to all relevant occurrences across both sets. For another digit locked in one ALS, check visibility to every occurrence of that digit in that particular ALS. Do not replace these occurrence tests with a rule about seeing every cell in the ring.
The logic
Whichever restricted common is used by one ALS, the other allocation is forced so that both ALSs become locked. Restricted-common candidates can be removed from cells that see all of their relevant occurrences across the sets. A non-RCC digit can be removed from a cell that sees all of its occurrences in the individual ALS that must contain it.