Swordfish

A Swordfish is a fish pattern extending the X-Wing concept to three rows and three columns. When a digit appears in at most three cells per row in exactly three rows, and all those cells align in the same three columns, the digit can be eliminated from other cells in those columns.

How It Works

The Pattern

Look for a digit that:

Important: Not every row needs to have candidates in all three columns. The pattern can be "incomplete" as long as the three rows together cover the three columns.

The Logic

The three rows collectively must place the digit somewhere in the three columns. Since there are exactly 3 rows and 3 columns, the digit is completely "covered" by these rows — no other cell in those columns can contain it.

How to Spot Swordfish

Single-Digit Focus

The key to spotting fish patterns is focusing on one digit at a time:

Fish Question What to Look For
X-Wing "Where can digit X go in each row?" 2 rows with same 2 columns
Swordfish "Where can digit X go in each row?" 3 rows with at most 3 columns
Jellyfish "Where can digit X go in each row?" 4 rows with at most 4 columns

Step-by-Step Scanning

  1. Pick a digit — Choose any digit 1-9
  2. Scan each row — For that digit, note which columns it can appear in
  3. Find restricted rows — Look for rows where the digit appears in only 2-3 columns
  4. Match columns — Do three rows share the same three columns (or subset)? That's a Swordfish!
  5. Eliminate — Remove the digit from other cells in those columns

Using Focus Mode

Focus Mode makes Swordfish much easier to spot:

  1. Tap a digit to highlight all cells containing it
  2. Look at each row — does the digit appear in 2-3 specific columns?
  3. Compare rows — do any three rows share candidates in the same three columns?
  4. If yes, check for eliminations in those columns

Example

Look at digit 8 and ask: where can 8 go in each column?

Column Analysis:

Since columns 1, 5, and 7 "cover" rows 2, 3, and 4, no other cell in those rows can contain 8.

Eliminations: Remove 8 from R2C2, R2C8, R3C2, R3C9, and R4C6

puzzle: S9B050b0i0d014y0g4y03624b0682cy0343bv02624b0302cy1ub71ubf4a0e0203b64bb707060f0c0g7n054b0bbfbf01094a0f0b07050c4a0c5u4j0z0f09040b5v022i17080c0z067n9f090f430g040b0c4305
mode: guided
technique: Swordfish
initial:
  layers:
    hints: true
steps:
  - text: >
      Use Focus Mode to highlight digit 8. Where can 8 go in each column?
    hint: subtle
    technique: SW
    state:
      focus:
        enabled: true
        digits: [8]

  - text: >
      Columns 1, 5, and 7 all have 8 confined to rows 2, 3, and 4!
    hint: obvious
    technique: SW
    state:
      selection:
        cells: [R2C1, R2C5, R2C7, R3C1, R3C5, R3C7, R4C1, R4C5, R4C7]
      focus:
        enabled: true
        digits: [8]

  - text: >
      Three columns with candidates in only three rows — this is a Swordfish!
    hint: obvious
    technique: SW
    state:
      selection:
        cells: [R2C1, R2C5, R2C7, R3C1, R3C5, R3C7, R4C1, R4C5, R4C7]
      focus:
        enabled: true
        digits: [8]

  - text: >
      Columns 1, 5, and 7 "cover" rows 2, 3, and 4. Eliminate 8 from other cells in these rows.
    hint: detailed
    technique: SW
    state:
      selection:
        cells: [R2C2, R2C8, R3C2, R3C9, R4C6]
      focus:
        enabled: true
        digits: [8]
settings:
  showCandidates: true
  showControls: true
  showDescription: true
  navigation: numbered

Incomplete Swordfish

A Swordfish doesn't require all 9 cells to have the candidate. Valid patterns include:

  C1  C5  C7
R2  8   8   8    (3 candidates)
R3  8   8   -    (2 candidates)
R4  8   -   8    (2 candidates)

As long as each row's candidates fall within the three columns, and each column is covered by at least one row, the pattern works.

View in cn-space

This is a column-based Swordfish: 3 columns confine a digit to the same 3 rows. In cn-space, this becomes a Naked Triple — 3 cells in a unit sharing 3 candidates.

An incomplete Swordfish (where some columns have the digit in only 2 of the 3 rows) appears as a Naked Triple where some cells have fewer than 3 candidates — which is perfectly normal for naked subsets.

puzzle: S9B050b0i0d014y0g4y03624b0682cy0343bv02624b0302cy1ub71ubf4a0e0203b64bb707060f0c0g7n054b0bbfbf01094a0f0b07050c4a0c5u4j0z0f09040b5v022i17080c0z067n9f090f430g040b0c4305
mode: guided
initial:
  layers:
    hints: false
steps:
  - text: >
      The Swordfish on digit 8: columns 1, 5, and 7 confine 8 to rows 2, 3, and 4.
    state:
      focus:
        enabled: true
        digits: [8]
      selection:
        cells: [R2C1, R2C5, R2C7, R3C1, R3C5, R3C7, R4C1, R4C5, R4C7]

  - text: >
      In **cn-space**, this becomes a Naked Triple — columns 1, 5, and 7 for digit 8 share candidates {R2, R3, R4}.
    state:
      space: cn
      focus:
        enabled: true
        digits: [2, 3, 4]
        multiDigitMode: 2+
      selection:
        cells: [D8C1, D8C5, D8C7]
settings:
  showCandidates: true
  showControls: true
  showDescription: true
  navigation: numbered

Tips

  1. Build from X-Wings — If you find an X-Wing that almost works, check if adding a third row/column completes a Swordfish
  2. Count carefully — Each row must have 2-3 candidates in the defining columns
  3. Works both ways — Can be row-based (define rows, eliminate from columns) or column-based
  4. Rare but powerful — Swordfish patterns are less common than X-Wings but often unlock stuck puzzles

The Fish Family

Fish Dimensions Max Cells
X-Wing 2 × 2 4
Swordfish 3 × 3 9
Jellyfish 4 × 4 16

The pattern generalises: N rows with candidates in only N columns = elimination from other cells in those columns.

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