GridWits
Expert tier Technique 15 of 46 Used by Smart Hint

Swordfish

X-Wing's three-line cousin: a digit's candidates across three rows fit inside the same three columns (or vice versa).

How it works

  1. 1Digit 8's candidates in row 1, row 4, and row 7 all fall inside columns B, E, and H — never more than that, and every row uses at least two of them.
  2. 2That's a Swordfish: across these three rows, 8 must occupy exactly those three columns. Any 8 elsewhere in columns B, E, or H can be eliminated — including all three cells in row 3 (B3, E3, H3).

Play a Sudoku that needs this technique →

A 1 B 2 C 3 D 4 E 5 F 6 G 7 H 8 I 9 3 8 5 8 7 8 1 8 3 8 2 8 6 8 8 9 4 8 8 8 8 8 8 8 8 8 8
  • Cells that establish the pattern
  • Where the conclusion lands
  • Candidate ruled out
Next in the ladder Gurth's Theorem →

On a puzzle built with 180°-rotational symmetry, the digit that would land on a cell's mirror-image partner must be its complement — narrowing candidates without touching any other unit.