An advanced pattern explained from the proof

X-Wing in Sudoku: why four aligned candidates remove others

Choose one candidate, such as 7. Suppose row 2 can place 7 in only columns 3 or 9, and row 8 has the same two choices. The two rows must use those two columns in some order.

One visible proof

The four candidates form a rectangle and reserve the digit in two columns. This pattern is called an X-Wing.

1. Choose one digitFollow candidate 7 only.
2. Find two matching rowsRows 2 and 8 each allow 7 in columns 3 and 9 only.
3. Clear the two columnsThose rows will supply the 7s for both columns, so other cells in the columns cannot contain 7.

Rows 2 and 8 restrict candidate 7 to the same two columns.

✓ If row 2 uses column 3, row 8 must use column 9. If row 2 uses column 9, row 8 must use column 3. Either way, both columns receive 7 inside the four corners.

Try it yourself

Use this reasoning on a fresh grid.

The interactive lesson shows one example, then lets you make the next check.

Open the interactive X-Wing lesson →No account needed. Your progress stays on this device.