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X-Wing

When two lines lock a candidate into the same two crossings.

Explanation

If a candidate appears in exactly the same two columns across two rows, those rows reserve the candidate at the crossings. The candidate can be removed from the other cells in those columns. The same logic also works with rows and columns swapped.

X-Wing example Sudoku board 5 3 6 9 2 1 9 5 3 8 8 4 5 7 8 5 6 1 4 2 3 2 3 9 1 9 2 8 6 9 6 5 2 4 2 8 7 4 3 4 5 2 7
An example board where X-Wing applies

Practice tip

Scan one digit at a time. X-Wings are easier to spot when candidate notes are already filled.

Example steps

  1. Pick one candidate and scan every row for exactly two positions.
  2. Find two rows that use the same two columns.
  3. Remove that candidate from the other cells in the crossing columns.

Try this technique on a real puzzle.

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