Four cells whose combined candidates span exactly four digits. The restricted common candidate is eliminated from cells seeing all its possible positions.
Look for four cells whose candidates together cover exactly four digits, with three of those digits confined so all their positions see one another. The fourth digit, the non-restricted common, must then land in one of the four cells. Eliminate it from any outside cell that sees every position it could take.
A WXYZ-Wing is the largest member of the Wing family (XY-Wing → XYZ-Wing → WXYZ-Wing). It involves four cells whose combined candidates cover exactly four digits {W, X, Y, Z}. One digit among these four is the "restricted common", it appears as a candidate in cells that are all visible to the elimination targets.
The logic extends from smaller wings, but the four cells are NOT a locked set (they don't all see each other), so it is not true that each digit goes in exactly one cell. Instead, the pattern works when every one of the four digits EXCEPT one is "restricted" — confined so that all of its positions among the four cells mutually see each other. The single leftover digit, the non-restricted common candidate Z, is then forced into one of the four cells, so any cell seeing all of Z's positions cannot itself be Z.
WXYZ-Wings are rare and hard to spot in practice. They represent an advanced pattern that most solvers encounter only in the hardest puzzles. Don't try to hunt for these, but recognize the logic if your solver or hint system points one out.
Find four cells whose combined candidate set contains exactly four digits. The cells don't all need to share a single unit, but the pattern must be connected, typically a pivot cell seeing three wings, or cells linked through shared units.
Identify the restricted common candidates: the shared digits whose occurrences among the four cells all see each other (share a common unit), so at most one cell can actually hold each. These are the forcing digits and are NOT eliminated. The one remaining shared digit whose positions do NOT all see each other is the non-restricted common Z — that is the digit you eliminate.
Any cell outside the pattern that can see every cell in the pattern containing the restricted digit cannot hold that digit. It's guaranteed to be in one of those pattern cells.
Example 1: WXYZ-Wing
Four cells form the pattern: pivot R6C3 {2, 3, 6, 8}, and wings R4C3 {3, 6}, R5C1 {2, 6}, R7C3 {6, 8}. Their combined candidates are exactly {2, 3, 6, 8}, four digits across four cells.
Three of the digits are restricted — each is confined so its positions mutually see: 2 (in R6C3 and R5C1, sharing box 4), 3 (in R6C3 and R4C3, sharing column 3), and 8 (in R6C3 and R7C3, sharing column 3). That leaves 6 as the non-restricted common, which must land in one of the four cells.
R5C3 sees all four pattern cells — R4C3, R6C3 and R7C3 down column 3, and R5C1 along row 5. Since one of those four must be 6, eliminate 6 from R5C3.
A WXYZ-Wing uses four cells spanning four digits, while an XYZ-Wing uses three cells spanning three digits: a three-candidate pivot plus two bivalue wings. Both eliminate a shared digit from cells that see every pattern cell holding it, but the WXYZ-Wing is the largest and rarest end of the Wing family (XY-Wing → XYZ-Wing → WXYZ-Wing).
A WXYZ-Wing eliminates the one digit that is not restricted. The three restricted digits are the forcing part of the pattern — each is confined so that all its positions among the four cells see one another — and they stay put. The leftover shared digit is the one forced into the pattern and removed from outside cells.
No, and that is what separates a WXYZ-Wing from a locked set. Because the four cells do not all share a unit, you cannot claim each digit occupies exactly one cell. The pattern instead needs the cells to be connected, typically a pivot seeing three wings, or cells linked through shared units.
Because the three restricted digits cannot fill all four cells. Each restricted digit has all its positions in the pattern seeing one another, so it can be used at most once among the four cells. Three restricted digits therefore cover at most three cells, and the fourth cell has to hold the remaining shared digit.
Find four connected cells whose combined candidate set contains exactly four digits, then test each shared digit to see whether all its positions among those cells see one another. Three must pass that test. Because they are rare and hard to spot, most solvers recognise the logic when a hint points one out rather than scanning for it.
Only to cells outside the pattern that see every pattern cell holding the non-restricted digit. In the worked example the four cells are R6C3, R4C3, R5C1 and R7C3, all carrying 6; R5C3 sees all four, so 6 comes out of R5C3 alone. One elimination is typical.
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