VWXYZ-Wing
A VWXYZ-Wing is a 5-cell ALS-XZ construction. Two almost locked sets share a restricted common candidate X and another digit Z. Because every X occurrence in one set sees every X occurrence in the other, both sets cannot use X. An external Z candidate that sees every Z occurrence in both sets can therefore be removed.
What is a VWXYZ-Wing?
An almost locked set of N cells contains exactly N+1 distinct candidates. A VWXYZ-Wing combines two such sets using one restricted common candidate X. The common 4+1 partition shown in this site’s example uses a 4-cell ALS and a bivalue ALS, but the partition is an example rather than the general definition.
How to spot it
Identify ALS A and ALS B, list each set’s distinct candidates, and find a shared digit X for which all X occurrences in A see all X occurrences in B. Then find another shared digit Z. A proposed target is valid only when it sees every Z occurrence in both sets. Do not require every cell in one ALS to see every cell in the other.
The logic
Assume an external target candidate Z is true. Z is then removed from both ALSs, turning each into a locked set. Each set would have to use X, but the restricted-common visibility forbids both sets from using X. The assumption is impossible, so the external Z candidate can be removed. The deduction does not remove a legitimate Z from either ALS.