Swordfish
Expert Removes candidates Used in: Sudoku, Killer Sudoku
The three-line cousin of the X-Wing. A digit’s candidates across three rows occupy the same three columns (two or three per row). The digit must fill those three columns from the rows, so it is removed from those columns elsewhere.
How to spot it
The X-Wing idea across three rows and three columns instead of two.
What you can conclude
Remove the digit from those three columns in every other row.
Worked example
Across three rows, 3 hides only in columns 1, 5 and 9; it must fill those columns from the rows, so remove 3 from them elsewhere.