Finned Swordfish: three-line fish with one escape

A finned Swordfish has three base rows and three cover columns, plus one extra base candidate outside the covers.

Key idea

A target is removable only when the standard Swordfish eliminates it and the fin also sees it.

See the move, step by step

Compare the 7 Swordfish with the fin at R1C2.

Step 1 of 4

Rows 1, 3, and 7 use cover columns 1, 3, and 6, except for one extra 7 in row 1.

Base rows and fin box

Step 2 of 4

The six cover candidates form the Swordfish. R1C2 is the single fin.

Near-SwordfishFish candidates and fin

Step 3 of 4

R2C3 is removed whether the fin is true or the underlying Swordfish is active.

Finned SwordfishCandidate to remove

Step 4 of 4

The fin blocks global cover-column eliminations; only the shared local target is updated.

Finned SwordfishUpdated target

Start from a valid Swordfish skeleton, then verify every elimination against both branches: fin true and fin false.