Hard Used from hard puzzles up.
Swordfish
An X-Wing over three lines
A Swordfish is an X-Wing with three rows and three columns: a digit whose candidates in three rows all fall within the same three columns.
The three rows need the digit three times, once in each of those columns, so the columns have it: remove it from their other cells.
A row may have the digit in only two of the three columns.
What to look for
Pick a digit and look for three rows (or columns) whose candidates for it share the same three columns.
Example
- The cells the technique relies on
- Cells where it removes candidates, struck out in red
Practise it
In the app, Learn › Swordfish sets exercises on real positions, then a full puzzle that needs this technique and nothing harder.