Lesson 26

WXYZ-Wing

The rule

A pivot and its three wings hold only four candidates between them, and the first three fit at most one cell each, so at least one cell holds the shared fourth, and any cell that sees all its possible spots loses that candidate.

Step by step

1. The pivot cell holds only candidates from 4, 7, 5 and 3, and it sees three bivalue wings: one with 4 and 3, one with 7 and 3, and one with 5 and 3. Together the four cells hold just those four candidates. This forms a WXYZ-Wing!
2. Each of 4, 7 and 5 fits at most one of the four cells, so at least one of the four cells must be 3. We can remove the candidate 3 from any other cell that sees every cell of the pattern holding the candidate 3.