X-Wing
X-Wing is an advanced elimination pattern where one digit appears in exactly two matching columns across two rows (or vice versa), creating a forced 2x2 structure.
Coordinates in this page use row letters A-I and column numbers 1-9 (for example B3).
Checklist before elimination
- For one digit, two rows each have exactly two candidate positions.
- Those positions are in the same two columns in both rows.
- Equivalent column-based form is also valid.
Steps
- Pick one digit and trace only that digit across the grid.
- Find rows (or columns) where the digit has exactly two candidates.
- Confirm two rows share the same two columns.
- Eliminate the digit from other cells in those two columns.
Search order for advanced grids
- Choose one difficult digit and inspect only that digit.
- List rows with exactly two candidate positions.
- Find matching column pairs and apply elimination narrowly.
Concrete example (valid)
Focus on digit 8. If row R2 has 8 only at C3/C7, and row R6 also has 8 only at C3/C7, an X-Wing is formed.
8
8
8
4
1
8
8
8
9
8
8
Keep Remove Focus Given Rows A-I / Columns 1-9
Blue cells are the four X-Wing corners. Red cells in the same columns are eliminated.
Invalid case (do not eliminate)
If R2 is C3/C7 but R6 is C3/C8, the column pairs do not match, so this is not an X-Wing.
8
8
8
4
1
8
8
9
8
Keep Remove Focus Given Rows A-I / Columns 1-9
The two rows do not share the same column pair, so no X-Wing can be applied.
Common mistakes
- Applying X-Wing when the 2x2 symmetry is incomplete.
- Removing candidates for digits other than the target digit.
- Eliminating outside the two target columns/rows.