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ADVANCED TECHNIQUE

X-Wing

Four corners of a rectangle, one digit, and a powerful elimination across the grid.

What is an X-Wing?

An X-Wing uses one digit across two rows. If, in each of the two rows, the digit has exactly two possible cells, and those cells are in the same two columns, they form the corners of a rectangle. The digit must sit on two opposite corners, either top-left and bottom-right or top-right and bottom-left. Either way, each of the two columns gets its digit from one of the two rows.

In rows 2 and 6, 4 can only go in columns 3 and 7. The four corners form an X-Wing, so 4 is removed from every other cell of columns 3 and 7. Only candidates for 4 are shown.

How to find an X-Wing

  1. Choose a digit and look at its candidates in every row.
  2. Find rows with exactly two candidates for that digit.
  3. Match two of them whose candidates are in the same two columns.
  4. Eliminate the digit from all other cells of those two columns.

The same pattern works with columns and rows swapped: two columns with the digit in the same two rows let you clear those rows.

Why it works

Row 2 needs a 4 in column 3 or column 7. If it takes column 3, then row 6 must take column 7, and the other way round. In both cases, columns 3 and 7 each receive their 4 from rows 2 and 6, so no other cell in those columns can hold a 4.

Practice x-wingTry the technique on a fresh Expert puzzle.
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GOOD TO KNOW

A little clarity
before you play.

The details, without the distractions.

Is X-Wing an advanced technique?

Yes. It is usually needed only on Expert puzzles, after singles, pairs, and pointing moves are exhausted.

What comes after X-Wing?

Swordfish (the same idea with three rows and three columns), XY-Wing, and chains are the next steps for very hard puzzles.

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