Hard Used from hard puzzles up.
X-Wing
Two rows, two columns
Take a digit with exactly two possible cells in each of two rows, in the same two columns: the four cells are the corners of a rectangle.
Whatever happens, the digit takes two opposite corners, one in each column. Both columns have it then: remove it from their other cells.
It works the same with columns and rows swapped.
What to look for
Pick a digit and look for two rows (or two columns) where it has exactly two places, lined up.
Example
- The cells the technique relies on
- Cells where it removes candidates, struck out in red
Practise it
In the app, Learn › X-Wing sets exercises on real positions, then a full puzzle that needs this technique and nothing harder.