Swordfish
Prerequisites: X-Wing
Overview
The Swordfish extends the X-Wing from two rows and two columns to three rows and three columns, allowing eliminations when a digit's candidates align across three rows.
How It Works
A Swordfish occurs when a digit has candidates in at most 3 positions in each of 3 rows, and all those positions fall within the same 3 columns. Since the digit must occupy exactly one cell in each row (and each column), it can be eliminated from all other cells in those 3 columns.
When To Use It
Look for Swordfish after checking for X-Wings. If a digit has 2-3 candidate positions per row in several rows, check whether three rows share the same three columns.
How To Detect It
For each digit, find rows where it has 2-3 candidate positions. Check combinations of three such rows — if all positions fall within exactly 3 columns, you have a Swordfish.
Visual Example
Step 1 of 10
X-Wing Extended to Three Rows
The Swordfish extends the X-Wing pattern from two rows and two columns to three rows and three columns. The logic is identical — a digit is forced into the same set of columns across multiple rows, locking it out of those columns elsewhere.
Candidates already ruled out by earlier techniques aren't shown.
Practice
Your goal: fill the highlighted cell. Select a cell, then pick a number.
A Swordfish on one digit is hiding here. Use it to eliminate, then fill the resulting Naked Single.
Use it in a real game
You'll rarely need this one, but Hard puzzles are where it can turn up.
Play a Hard puzzle