Swordfish

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Swordfish

What It Is

Swordfish extends X-Wing to three rows and three columns. If a candidate appears in at most three positions in three rows and those positions share the same three columns, each column will contain that candidate in those rows, allowing eliminations elsewhere.

When to Use

Hard puzzles when X-Wings fail; scan a single digit across all rows/columns in mid-to-late game.

How to Apply (Step-by-Step)

  1. Pick a candidate number and note rows where it remains.
  2. Find three rows with the candidate in up to three cells, aligned in the same three columns.
  3. Verify each involved column has the candidate only in those rows.
  4. Eliminate outside the fish: remove the candidate from other cells in those columns.
  5. Re-scan for singles or simplified patterns.

If 4 is in columns 3,5,7 across rows 2,5,8 only, clear 4 from other cells in columns 3,5,7; the swordfish spears those candidates.

See also

Scanning / Cross-Hatching Single Candidate (Naked Single) Single Position (Hidden Single) Naked Pairs / Triples / Quads Hidden Pairs / Triples / Quads Pointing Pairs / Triples (Locked Candidates Type 1) Box–Line Reduction (Locked Candidates Type 2) X-Wing Swordfish Jellyfish XY-Wing XYZ-Wing W-Wing Alternating Inference Chains (AICs) Forcing Chains / Forcing Nets Nishio Coloring Multi-Coloring Uniqueness Techniques (Unique Rectangle etc.) Fish Variants (Finned X-Wing, Sashimi etc.) ALS Techniques (ALS-XZ, ALS Chains) Sue de Coq Pattern Overlay / Template Method
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