Swordfish Technique
advancedExtension of X-Wing to three rows and three columns
The Swordfish extends the X-Wing concept from a 2x2 fish to a 3x3 fish. A candidate is confined to at most three columns across three rows, allowing eliminations in those columns.
Understanding the Concept
Select three rows where a candidate appears 2-3 times in each row, and all occurrences fall within the same three columns.
Not every intersection needs to be occupied — you just need the candidate confined to those three columns across all three rows.
By the same pigeonhole logic as X-Wing, one instance per row must fill those columns, so all three columns are "claimed."
Eliminate the candidate from every other cell in those three columns that is not in the pattern rows.
The transposed version works identically: three columns confining to three rows, with eliminations in the rows.
Swordfish is much rarer than X-Wing but follows exactly the same reasoning extended by one dimension.
Examples
Swordfish on Digit 4 (Rows 1, 4, 7 / Columns 0, 3, 8)
Digit 4 in row 1 appears only at columns 0 and 3; in row 4 only at columns 0, 3, and 8; in row 7 only at columns 3 and 8. All occurrences are confined to columns 0, 3, and 8. Therefore, 4 can be eliminated from all other cells in those three columns. Blue cells show the Swordfish pattern; red cells show eliminations.
Pro Tips
- •Start by finding rows where a candidate appears in only 2 or 3 cells
- •Check whether three such rows confine the candidate to the same three columns
- •Not all nine intersections need to contain the candidate — just a subset
- •Swordfish is quite rare; most puzzles are solvable without it
- •Master X-Wing first, then the Swordfish logic is a natural extension
