X-Wing
When a digit is confined to the same two columns in two rows, it forms a rectangle and can be removed from those columns elsewhere.
When to use it
Use when a single candidate appears in exactly the same two columns across two rows (or the same two rows across two columns).
Worked example
-
Candidate 4 appears in only two columns across two rows, forming a rectangle.
-
The 4 must take opposite corners, so it is removed from those two columns in every other row.
Common mistakes
- Allowing the digit in a third column of either row — the candidates must line up in exactly two columns.
- Eliminating along the rows: when the base sets are rows, the eliminations happen down the columns.
Frequently asked questions
What is an X-Wing in Sudoku?
A pattern where a digit is restricted to the same two columns in two rows. It must occupy opposite corners, so the digit is cleared from those columns in the other rows.