Overview
- Tier 4
- Fish, wings, chains & uniqueness
- Typical difficulty
- Peak Score 60–75
- Also known as
- 3-Fish, Three-Line Fish
A Swordfish occurs when a candidate digit in three rows is confined to at most three columns. The digit can be eliminated from all other cells in those three columns.
The Swordfish extends the X-Wing logic into three dimensions of lines. In three separate rows, a candidate appears in cells that collectively belong to only three columns. Because each of the three rows must contain the digit, and no two can share a column, the digit must occupy one cell in each of the three columns. Consequently, no other cells in those three columns can hold that candidate.
Worked examples
1 / 5
Reading the exampleCells forming the patternCells losing candidatesEliminated candidates
157
6
1257
258
289
2589
3
257
4
4
8
257
3
26
1
9
2567
27
3
9
25
256
7
4
8
256
1
158
2
4
9
3
578
15
178
6
158
7
6
258
14
258
145
9
3
9
3
158
578
14
6
2
1478
78
6
4
9
1
5
3
7
28
28
78
15
78
4
269
29
16
3
59
2
15
3
678
689
789
146
14
59
In rows 2, 3 and 6, the digit 5 can only go in columns 3, 4 and 8. The three rows take one 5 in each of those columns, so 5 can be removed from the rest of columns 3, 4 and 8.
Removes: 5 from R1C3, R1C4, R5C4, R1C8
How to apply it
Spotting the pattern and making the deduction, in order.
- Select a digit and find three separate rows where it only appears in two or three cells.
- Verify that across all three rows, the candidate cells only fall into three shared columns.
- Because each of the three rows must contain the digit, and no two can share a column, the digit must occupy one cell in each of the three columns.
- The digit is completely locked into those three columns across the three rows.
- Eliminate that candidate from every other cell along those three columns.
Common mistakes
- Having candidate cells in a fourth column in one of the three rows.
- Thinking each row must contain all three columns; having only 2 candidate cells per row is common and fully valid.
- Failing to check for column-based Swordfish (where 3 columns project onto 3 rows).
Frequently asked questions
- How many cells make up a Swordfish?
- A Swordfish can consist of anywhere from 6 to 9 cells (minimum 2 per row across 3 rows).
- Is Swordfish common in daily puzzles?
- Swordfish appears regularly in Tough and Expert puzzles. Recognizing it is essential for solving without guessing.
Related techniques
Put Swordfish into practice
Try a puzzle from the Tough tier (Peak Score 61–70).