Squirmbag

Level 9 · Purple 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

Look for Squirmbag.

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

1

Squirmbag

Check digit 8 in rows 3, 4, 6, 7 and 8.

Sudoku grid illustrating step 1: Squirmbag — Check digit 8 in rows 3, 4, 6, 7 and 8.

2

Squirmbag

r3c3 is already filled with 5.

Sudoku grid illustrating step 2: Squirmbag — r3c3 is already filled with 5.

3

Squirmbag

Digit 8 cannot go in r3c4 because r5c4 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 3: Squirmbag — Digit 8 cannot go in r3c4 because r5c4 is already in this column. Remove the entry or choose a different digit.

4

Squirmbag

r3c7 is already filled with 6.

Sudoku grid illustrating step 4: Squirmbag — r3c7 is already filled with 6.

5

Squirmbag

r3c8 is already filled with 2.

Sudoku grid illustrating step 5: Squirmbag — r3c8 is already filled with 2.

6

Squirmbag

r4c3 is already filled with 9.

Sudoku grid illustrating step 6: Squirmbag — r4c3 is already filled with 9.

7

Squirmbag

r4c4 is already filled with 5.

Sudoku grid illustrating step 7: Squirmbag — r4c4 is already filled with 5.

8

Squirmbag

r4c7 is already filled with 7.

Sudoku grid illustrating step 8: Squirmbag — r4c7 is already filled with 7.

9

Squirmbag

Digit 8 cannot go in r4c8 because r9c8 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 9: Squirmbag — Digit 8 cannot go in r4c8 because r9c8 is already in this column. Remove the entry or choose a different digit.

10

Squirmbag

r6c3 is already filled with 6.

Sudoku grid illustrating step 10: Squirmbag — r6c3 is already filled with 6.

11

Squirmbag

Digit 8 cannot go in r6c4 because r5c4 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 11: Squirmbag — Digit 8 cannot go in r6c4 because r5c4 is already in this column. Remove the entry or choose a different digit.

12

Squirmbag

r6c7 is already filled with 9.

Sudoku grid illustrating step 12: Squirmbag — r6c7 is already filled with 9.

13

Squirmbag

Digit 8 cannot go in r6c8 because r9c8 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 13: Squirmbag — Digit 8 cannot go in r6c8 because r9c8 is already in this column. Remove the entry or choose a different digit.

14

Squirmbag

r7c3 is already filled with 4.

Sudoku grid illustrating step 14: Squirmbag — r7c3 is already filled with 4.

15

Squirmbag

r7c4 is already filled with 2.

Sudoku grid illustrating step 15: Squirmbag — r7c4 is already filled with 2.

16

Squirmbag

r7c7 is already filled with 1.

Sudoku grid illustrating step 16: Squirmbag — r7c7 is already filled with 1.

17

Squirmbag

Digit 8 cannot go in r7c8 because r9c8 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 17: Squirmbag — Digit 8 cannot go in r7c8 because r9c8 is already in this column. Remove the entry or choose a different digit.

18

Squirmbag

r8c3 is already filled with 2.

Sudoku grid illustrating step 18: Squirmbag — r8c3 is already filled with 2.

19

Squirmbag

r8c4 is already filled with 6.

Sudoku grid illustrating step 19: Squirmbag — r8c4 is already filled with 6.

20

Squirmbag

Digit 8 cannot go in r8c7 because r9c8 is already in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 20: Squirmbag — Digit 8 cannot go in r8c7 because r9c8 is already in this box. Remove the entry or choose a different digit.

21

Squirmbag

r8c8 is already filled with 7.

Sudoku grid illustrating step 21: Squirmbag — r8c8 is already filled with 7.

22

Squirmbag

In each of these 5 rows, digit 8 is restricted to the same 5 columns: 1, 2, 5, 6 and 9.

Sudoku grid illustrating step 22: Squirmbag — In each of these 5 rows, digit 8 is restricted to the same 5 columns: 1, 2, 5, 6 and 9.

23

Squirmbag

That creates a Squirmbag: those columns must contain the digit for these rows, so other rows cannot keep it there.

Sudoku grid illustrating step 23: Squirmbag — That creates a Squirmbag: those columns must contain the digit for these rows, so other rows cannot keep it there.

24

Squirmbag

These are the extra 8 candidates in columns 1, 2, 5, 6 and 9 that must be removed: r2c1 and r2c6.

Sudoku grid illustrating step 24: Squirmbag — These are the extra 8 candidates in columns 1, 2, 5, 6 and 9 that must be removed: r2c1 and r2c6.

25

Squirmbag

Remove 8 from the extra cells in columns 1, 2, 5, 6 and 9: r2c1 and r2c6.

Sudoku grid illustrating step 25: Squirmbag — Remove 8 from the extra cells in columns 1, 2, 5, 6 and 9: r2c1 and r2c6.

26

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.