Ninesmith Sudoku Polski Get the app

Sudoku techniques

The Y-Wing

The Y-Wing uses three cells with two candidates each. Whichever digit the middle cell takes, one of the other two ends up with the same digit, so any cell that sees both of them can't have it.

Ninesmith Sudoku ·

In short

  • A pivot cell with two candidates, A and B, sees two pincer cells: one with A and C, one with B and C.
  • If the pivot is A, one pincer is C. If it's B, the other pincer is C.
  • So C comes out of every cell that sees both pincers.
  • Also called the XY-Wing.

An example

A position from a real puzzle. The pivot at row 1, column 8 holds 6 or 9. It sees row 3, column 9 (7 or 9) in its box, and row 8, column 8 (6 or 7) in its column. If the pivot is 9, row 3, column 9 is 7; if it is 6, row 8, column 8 is 7. Either way one of them is 7, so 7 comes out of the four cells that see both.

The four cells are row 3, column 8 and, in column 9, rows 7, 8 and 9. Row 7, column 9 held 7 or 9, so after the Y-Wing it is a 9: the pattern places a digit one step later.

How to find one

  1. Look at cells with exactly two candidates. Pick one as the pivot, say 6 and 9.
  2. Among the two-candidate cells it sees, find one with 9 and something else, C, and another with 6 and the same C.
  3. The two pincers must not share a house with each other; if they did, it would be a simpler pattern.
  4. Strike C from every cell that sees both pincers.

Why it works

The pivot is A or B, nothing else. Each choice forces one pincer to C. A cell that sees both pincers would clash with whichever one became C, so it can't be C either way.

Questions

What is a Y-Wing in Sudoku?

Three two-candidate cells, AB, AC and BC, where AB sees the other two. Any cell that sees both AC and BC can't be C.

Is a Y-Wing the same as an XY-Wing?

Yes, they are two names for the same pattern.

Does the pivot have to share a box with a pincer?

No. The pivot has to see each pincer through any house: a row, a column or a box.

Next: Unique Rectangle · all techniques

Drill the Y-Wing with the Smith

Ninesmith Sudoku is a calm Sudoku app for iPhone. Its Pattern Trainer drills the Y-Wing in sessions of 30 to 90 seconds, and in your own puzzles the Smith names the technique and shows the pattern before anything goes in.

Get the app

The full Y-Wing drills are part of Premium; the first scenario is free. No ads in any tier.