How it works
Swordfish extends X-wing from two rows to three. The digit must have its candidate cells across three rows confined to the same three columns. The shape can be irregular; it does not have to be a clean rectangle.
The conclusion is the same: those three rows commit to three cells, those three cells distribute across three columns, and the digit cannot appear elsewhere in those columns.
Swordfish is harder to spot because the candidate cells may not visually line up. Tracking digit positions on a separate sheet (or in your head) is the only reliable way.
When to look for it
When X-wing searches come up empty. Swordfish is rare but devastating when it applies.
Tips for spotting the pattern
- Each of the three rows must have only two or three candidates for the digit, all within the same three columns.
- If you find a swordfish but no eliminations follow, the digit was already constrained.
- Swordfish in columns work the same way. Scan both directions.
Common mistakes
- Including a row where the digit has four candidates. Swordfish requires 2 or 3 per row.
- Allowing the three columns to be different from row to row. The columns must be the same set across all three rows.
- Eliminating from the rows instead of the columns. The eliminations sweep the columns outside the swordfish.