X-Wing
A rectangle of four candidate cells for one digit that eliminates that digit from two crossing lines.
The X-Wing is the gateway to advanced solving. Look at a single digit across two rows: if in both rows the digit can go in only the same two columns, those four cells form a rectangle. The digit must occupy opposite corners of the rectangle, which lets you eliminate it from the rest of those two columns.
The same pattern works with the roles of rows and columns swapped.
How to spot it
Choose a digit. Find two rows in which the digit has exactly two candidate cells, and those candidates share the same two columns. Whichever diagonal the digit takes, both of those columns are covered — so remove the digit from those two columns in every other row.
- One digit, two rows with only two candidate cells each.
- The candidate columns match across both rows.
- Eliminate the digit elsewhere in those two columns.
Rows or columns
An X-Wing can be defined on rows (eliminating along columns) or on columns (eliminating along rows). Scan both orientations when hunting for it.
Worked example
- For digit 6, row 2 allows 6 only in columns 3 and 7.
- Row 8 also allows 6 only in columns 3 and 7.
- These four cells form an X-Wing rectangle.
- Whatever the layout, columns 3 and 7 get their 6 from rows 2 and 8.
- Remove 6 from columns 3 and 7 in all other rows.
Try it yourself
Tap a cell, then a number, to practise.
Frequently asked questions
- Why is it called X-Wing?
- Because the two valid placements lie on a diagonal across the rectangle, forming an X of mutually exclusive options.
Related techniques
Practice: X-Wing
Put the X-Wing to work on a live board — free puzzles with notes, hints and four difficulty levels.
Try it on a live board