Squirmbag

Level 11 · Red Belt

Strategy:

Requires:

Learn after:

Finned Squirmbag

Overview

Squirmbag (or Sixfish) is a five-row, five-column fish pattern. It's extremely rare and only appears in very difficult puzzles.

How It Works

Find five rows where a candidate is restricted to the same five columns.
Each row must have the candidate in 2-5 cells within these columns.
Eliminate the candidate from other cells in those five columns.

Example

Starting position

Look for Squirmbag.

Sudoku grid showing the initial puzzle state for Look for Squirmbag.

1

Scan base rows 1, 2, 5, 6 and 7 for 2

Base rows: 1, 2, 5, 6 and 7. Check where digit 2 can appear in those rows.

Sudoku grid illustrating step 1: Scan base rows 1, 2, 5, 6 and 7 for 2 — Base rows: 1, 2, 5, 6 and 7. Check where digit 2 can appear in those rows.

2

r1c2 is already filled

r1c2 is already filled with 1.

Sudoku grid illustrating step 2: r1c2 is already filled — r1c2 is already filled with 1.

3

r1c3 is already filled

r1c3 is already filled with 4.

Sudoku grid illustrating step 3: r1c3 is already filled — r1c3 is already filled with 4.

4

r1c8 is already filled

r1c8 is already filled with 5.

Sudoku grid illustrating step 4: r1c8 is already filled — r1c8 is already filled with 5.

5

r1c9 is already filled

r1c9 is already filled with 8.

Sudoku grid illustrating step 5: r1c9 is already filled — r1c9 is already filled with 8.

6

2 is blocked from r2c2 by the column

Digit 2 cannot go in r2c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 6: 2 is blocked from r2c2 by the column — Digit 2 cannot go in r2c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

7

2 is blocked from r2c3 by the box

Digit 2 cannot go in r2c3 because r3c2 is already in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 7: 2 is blocked from r2c3 by the box — Digit 2 cannot go in r2c3 because r3c2 is already in this box. Remove the entry or choose a different digit.

8

r2c8 is already filled

r2c8 is already filled with 9.

Sudoku grid illustrating step 8: r2c8 is already filled — r2c8 is already filled with 9.

9

r2c9 is already filled

r2c9 is already filled with 1.

Sudoku grid illustrating step 9: r2c9 is already filled — r2c9 is already filled with 1.

10

2 is blocked from r5c2 by the column

Digit 2 cannot go in r5c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 10: 2 is blocked from r5c2 by the column — Digit 2 cannot go in r5c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

11

r5c3 is already filled

r5c3 is already filled with 6.

Sudoku grid illustrating step 11: r5c3 is already filled — r5c3 is already filled with 6.

12

r5c8 is already filled

r5c8 is already filled with 7.

Sudoku grid illustrating step 12: r5c8 is already filled — r5c8 is already filled with 7.

13

2 is blocked from r5c9 by the column

Digit 2 cannot go in r5c9 because r4c9 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 13: 2 is blocked from r5c9 by the column — Digit 2 cannot go in r5c9 because r4c9 is already in this column. Remove the entry or choose a different digit.

14

2 is blocked from r6c2 by the column

Digit 2 cannot go in r6c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 14: 2 is blocked from r6c2 by the column — Digit 2 cannot go in r6c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

15

r6c3 is already filled

r6c3 is already filled with 7.

Sudoku grid illustrating step 15: r6c3 is already filled — r6c3 is already filled with 7.

16

2 is blocked from r6c8 by the box

Digit 2 cannot go in r6c8 because r4c9 is already in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 16: 2 is blocked from r6c8 by the box — Digit 2 cannot go in r6c8 because r4c9 is already in this box. Remove the entry or choose a different digit.

17

2 is blocked from r6c9 by the column

Digit 2 cannot go in r6c9 because r4c9 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 17: 2 is blocked from r6c9 by the column — Digit 2 cannot go in r6c9 because r4c9 is already in this column. Remove the entry or choose a different digit.

18

r7c2 is already filled

r7c2 is already filled with 7.

Sudoku grid illustrating step 18: r7c2 is already filled — r7c2 is already filled with 7.

19

r7c3 is already filled

r7c3 is already filled with 1.

Sudoku grid illustrating step 19: r7c3 is already filled — r7c3 is already filled with 1.

20

r7c8 is already filled

r7c8 is already filled with 8.

Sudoku grid illustrating step 20: r7c8 is already filled — r7c8 is already filled with 8.

21

r7c9 is already filled

r7c9 is already filled with 6.

Sudoku grid illustrating step 21: r7c9 is already filled — r7c9 is already filled with 6.

22

2 is confined to columns 1, 4, 5, 6 and 7

In each of these 5 rows, digit 2 is confined to the same 5 cover columns: 1, 4, 5, 6 and 7.

Sudoku grid illustrating step 22: 2 is confined to columns 1, 4, 5, 6 and 7 — In each of these 5 rows, digit 2 is confined to the same 5 cover columns: 1, 4, 5, 6 and 7.

23

The pattern forms a Squirmbag

That forms a Squirmbag: the cover columns must hold the digit for the base rows, so other rows cannot keep it there.

Sudoku grid illustrating step 23: The pattern forms a Squirmbag — That forms a Squirmbag: the cover columns must hold the digit for the base rows, so other rows cannot keep it there.

24

Extra 2 candidates in columns 1, 4, 5, 6 and 7

These are the extra 2 candidates in columns 1, 4, 5, 6 and 7 that must be removed: r9c1.

Sudoku grid illustrating step 24: Extra 2 candidates in columns 1, 4, 5, 6 and 7 — These are the extra 2 candidates in columns 1, 4, 5, 6 and 7 that must be removed: r9c1.

25

Remove 2 from columns 1, 4, 5, 6 and 7

Remove 2 from the extra cells in columns 1, 4, 5, 6 and 7: r9c1.

Sudoku grid illustrating step 25: Remove 2 from columns 1, 4, 5, 6 and 7 — Remove 2 from the extra cells in columns 1, 4, 5, 6 and 7: r9c1.

26

Result

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Squirmbags are extremely rare in hand-solvable puzzles.
If you find yourself looking for Squirmbags, the puzzle is very difficult.
Computer solvers are typically needed to reliably find these.