Swordfish
ExpertA swordfish is an X-wing with three rows. Take one digit: if, in three rows, its places all fall in the same three columns (two or three places per row), those rows use up the digit in those columns. The rest of the three columns can’t have it.
How to spot it
- Pick one digit and find rows where it has only two or three places.
- Find three of them whose places, together, cover only three columns.
- Remove the digit from every other cell of those three columns.
Why it works
The three rows each need the digit once, in three different columns, and they only have those three columns between them. So each of the three columns gets its digit from these rows.
Example
2
8
4
8
1
4
6
9
5
4
8
1
9
6
4
8
4
2
8
1
7
7
6
2
4
1
2
4
6
3
7
6
8
1
5
7
Look at the 9s in row 3, row 6, and row 8.
Common mistakes
- Letting the three rows cover a fourth column.
- Removing the digit from the three rows themselves.