An advanced technique extending X-Wing to 3 rows by 3 columns. Applicable when candidates in 3 rows are confined to at most 3 columns.

Swordfish is a generalization of X-Wing. When a specific digit's candidate positions across three rows are confined to a total of three columns or fewer, that digit can be eliminated from all other cells in those three columns. Sometimes required at Extreme difficulty.

Relationship to X-Wing

X-Wing is a 2-row by 2-column pattern, while Swordfish extends this to 3 rows by 3 columns. Each row may have candidates in 2-3 positions, as long as the total spans at most 3 columns. Not every row needs to have candidates in all 3 columns.

Practical Detection

Finding a Swordfish is extremely difficult, and most players stick to difficulty levels that do not require it. To find one, list the candidate column positions for a specific digit in each row, then look for a combination of 3 rows whose column positions span 3 or fewer columns.