Lesson 32

Finned Swordfish

The rule

A fin is one extra cell on a base line that stops a Swordfish from being complete, so the candidate is removed only from cells in the fin's box, outside the base lines, that lie on one of the Swordfish's three crossing lines.

Step by step

1. 9 almost forms a Swordfish in three base rows. If one extra cell were not there, every 9 candidate in those rows would sit in one of only three columns. That one extra cell is the fin.
2. Either 9 is in the fin, or the Swordfish is complete. Either way we can remove the candidate 9 from the cells of the fin's box that lie in one of the three columns and outside the three base rows.