Variant Sudoku

XY-Wing

A middle cell with candidates AB sees two wings, one AC and one BC. One wing must be C, so any cell that sees both wings can’t be C.

Practice now
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Clear 3 from cells that see both wings.

Why it works

On the board above:

r2c2 can only be 2 or 4.

If r2c2 is 2, then r3c3 (2 or 3) can’t be 2, so it is 3.

If r2c2 is 4, then r2c7 (4 or 3) can’t be 4, so it is 3.

Either way, r3c3 or r2c7 is 3. r3c7 sees both, so it can’t be 3.

How to spot it

  1. Find a middle cell with two candidates

    Call its digits A and B.

  2. Find two wings it sees

    Each wing has two candidates: one shared with the middle, plus a third digit.

  3. Check the wings share that third digit

    That digit is C. The wings must not both hold A, or both hold B.

  4. Clear C from cells that see both wings

    Look where the rows, columns and boxes of the two wings overlap.

Practice

Real boards from the solver, with every pencil mark filled in. Spot it, then use it, then find it cold.

Loading the boards…

Try it in a real puzzle

Each of these needs an XY-Wing to finish. It opens in the player.

Tips

All three cells have exactly two marks

If the middle has three, look at XYZ-Wing instead.

Wings can be far apart

One wing can share a row with the middle and the other a box.

XYZ-WingLike an XY-Wing, but the middle cell holds all three digits. The cell to clear must see all three.Next: XYZ-Wing →

In the glossary

XY-wing