Finned Swordfish

Prerequisites

Be comfortable marking candidates and proving an X-Wing and a regular Swordfish. You should be able to name the three base lines, the three cover lines and the 3×3 box containing the extra candidate.

Why the fin changes the Swordfish

A regular Swordfish confines one digit to three cover lines across three base lines. A Finned Swordfish has one or more extra candidates outside those cover lines, with every fin confined to the same 3×3 box as one corner of the underlying fish.

If the fin is false, the regular Swordfish removes the digit from its cover lines. If the fin is true, a target that sees the fin cannot contain the digit. A target is removable only when it lies on the affected cover line, inside the fin's box, and sees every possible fin.

Validated visual example and Genius Coach

The interactive candidate grid below is a real, uniquely solved catalogue position—not a decorative diagram. Its next step is recomputed by the same deterministic engine used by Genius Coach. Select the target cell and candidate, then prove the elimination yourself or reveal the five coaching levels one at a time.

Finned Swordfish mistakes to avoid

• Do not eliminate from every cover-line cell as though the fin did not exist.
• Do not combine fins from different boxes into one pattern.
• Do not remove a candidate that cannot see every fin.
• Check for a simpler X-Wing or regular Swordfish before using the finned form.

Continue through the fish family

Fish techniques use the same base-line and cover-line idea at different sizes. Follow the sequence to understand exactly what changes before attempting a harder pattern.