Swordfish

Swordfish is the 3-row version of X-Wing. Three rows each have a digit's candidates confined to a set of (up to three) columns whose union is exactly three columns. The digit must appear once in each of those rows — so it occupies the three columns one per row. It can be removed from those three columns elsewhere.

Each row doesn't have to use all three columns. It just needs to use only columns from the chosen three.

When to look for it

Swordfish are rarer than X-Wings but appear on tough puzzles. They're easier to spot if you've been tracking digit-by-row candidate maps.

How to apply it

1. Pick a digit.
2. For each row, list the columns where the digit can still go.
3. Find three rows whose column lists together use exactly three columns.
4. Eliminate the digit from those three columns in every other row.

Example