Jellyfish

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Jellyfish

What It Is

Jellyfish scales fish logic to four rows and four columns. If a candidate appears in at most four positions across four rows and those positions share four columns, each column will take that candidate in those rows, allowing eliminations elsewhere.

When to Use

Rare, very difficult puzzles after X-Wing and Swordfish; scan late-game candidates for 4×4 alignment.

How to Apply (Step-by-Step)

  1. For each digit, list rows and columns of its candidates.
  2. Identify four rows with the candidate in no more than four cells total, all within the same four columns.
  3. Confirm each column has the candidate only in those rows.
  4. Eliminate outside: remove the candidate from other cells in the four columns.
  5. Clean up and repeat if needed.

If digit 6 appears only in four spots across rows 2,4,6,8 and columns 3,4,6,9, clear 6 from other cells in those columns; the jellyfish nets the extras.

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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