Swordfish
A three-line generalisation of the X-Wing for a single digit, eliminating it across three crossing lines.
Swordfish extends the X-Wing idea from two lines to three. For one digit, find three rows where the digit’s candidates are confined to the same set of three columns. The nine-cell pattern forces the digit onto those columns in those rows, allowing eliminations elsewhere in the three columns.
Crucially, each row need not use all three columns — two of the three is enough, as long as the columns across the three rows total exactly three.
How to spot it
Pick a digit and look for three rows whose candidate cells for it lie within a common set of three columns. Then remove the digit from those three columns in every other row. As always, the column-based mirror image also works.
- One digit, three rows.
- Candidates confined to three shared columns.
- Eliminate the digit from those columns in other rows.
Worked example
- Digit 3 in rows 1, 5 and 9 only appears in columns 2, 4 and 8.
- No row uses a fourth column for 3.
- These cells form a swordfish on columns 2, 4 and 8.
- Remove 3 from those three columns in rows 2,3,4,6,7,8.
- Hidden singles for 3 typically follow.
Try it yourself
Tap a cell, then a number, to practise.
Frequently asked questions
- Does every row need three candidates?
- No. Each row may have two or three candidate cells; only the union of columns across the three rows must equal three.
- Is swordfish harder than X-Wing?
- It is harder to spot because the pattern is larger and the cells are sparser, but the logic is identical.
Related techniques
Practice: Swordfish
Put the Swordfish to work on a live board — free puzzles with notes, hints and four difficulty levels.
Try it on a live board