Proven Sudoku
WXYZ-Wing
Also called Four-cell wing, ALS-XZ of size 4 (loose usage).
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Four squares holding four numbers between them. Three of the numbers are stuck inside one row, column or box. The fourth is not. That fourth number has to land in one of these squares, so squares that see all its homes lose it.
The exact rule, for stronger players
The rule, stated exactly: Four cells spanning four digits {w,x,y,z} with z the only digit not restricted to a single house among them. Then z is eliminated from cells seeing every cell of the set that contains z.
What it removes: Remove z from cells seeing every z-bearing cell of the set.
Why it works: The four cells form an almost-locked set: four cells with five candidate slots across four digits. z is the restricted common candidate, so it must be placed inside the set, excluding it from anything seeing all its positions.
Worked examples
None yet. This pattern does not turn up in our daily boards, so there is no real example to show. We would rather wait than draw a fake one.
Learn these first
- XYZ-WingLike the XY-Wing, but the middle square has three numbers instead of two.
Related wings
- XY-WingThree squares, each with two numbers left.
- Bent Naked SubsetA group of squares bent across two rows, columns or boxes.
- Letter-named wings (M, S, L, H, Split, Hybrid, Local)Short chains that people gave letters to.
- Remote PairsA string of squares that all hold the same two numbers, each one linked to the next.
- VWXYZ-WingThe same idea stretched to five squares and five numbers.
How often does it come up?
Our rough estimate: uncommon. Most instances are found faster as an ALS-XZ once a solver knows ALS theory.