Lesson 15

Swordfish

The rule

When a number's candidates in three rows all fall within the same three columns (or in three columns all fall within the same three rows), that candidate is removed everywhere else in those three crossing lines.

Step by step

1. In each base row, 5 is a candidate in 2 or 3 cells. Taking the three base rows together, every 5 candidate sits in one of only three columns. This is a Swordfish!
2. The Swordfish means we can remove the candidate 5 from the three columns that hold it, in every cell outside the three base rows.