Example of Rows and Columns (Double)
- aka "X-Wing"

This is a screenshot

Rows and Columns (Double):
Occurances of a particular Possible
occur just twice in their Rows
and are also aligned in Columns
(or appear just twice in their Columns and are also aligned in Rows).In this example, the 9's (coloured purple) occur just twice in their Columns and are also aligned in Rows.

Because of this, for each of the Columns 2 and 5, there are only two Squares where a 9 can be a Solution - namely those in Rows A and J.

If the 9 for Column 2 is in Row A, then there is only one Square left for the remaining Column - that for Row J.

Because there is now a 9 in place for Rows A and J, there cannot be any other 9's in those Rows.

The 9's in A1, A6 and J4 (outlined in orange) are impossible solutions and may be removed.

This logic works whatever order you choose the Rows and Columns.