WXYZ-Wing: find one restricted common digit
A WXYZ-Wing is four cells whose combined candidates are exactly four digits, with one digit restricted so all of its occurrences see each other.
Key idea
One pattern cell must contain that restricted common digit. Any outside candidate seeing every occurrence of it can be removed.
See the move, step by step
Use four cells across rows 1 and 3 to restrict candidate 7.
Step 1 of 4
Find four cells using four digits
The pattern cells collectively use only 6, 7, 8, and 9 across two connected regions.
Step 2 of 4
Identify the restricted common candidate
Candidate 7 appears at R1C6 and R3C8, and those two cells see each other through box 3.
Step 3 of 4
Find a peer of every restricted 7
R3C6 sees both R1C6 and R3C8, so its 7 would conflict whichever pattern cell supplies 7.
Step 4 of 4
Keep the four-cell set
Remove 7 from R3C6 and leave the WXYZ-Wing unresolved.
Try it on today's puzzle
First verify the union contains exactly four digits. Then prove the elimination digit is restricted common and that the target sees every one of its occurrences.
Play today