Finned X-Wing

Level 7 · Green Belt

Strategy:

Finned & Sashimi Fish

Requires:

Learn after:

Finned Swordfish Sashimi X-Wing

Overview

A Finned X-Wing is an X-Wing with extra candidates (the "fin") in one of the base rows/columns. The fin restricts eliminations to cells that see both the fin and the normal elimination zone.

How It Works

Find an X-Wing pattern where one row has extra occurrences of the candidate.
These extra cells are the "fin".
Eliminations occur only in cells that see both the X-Wing column and the fin.

Example

Look for Finned X-Wing.

Sudoku grid showing the initial puzzle state for Look for Finned X-Wing.

1

Finned X-Wing

Check digit 3 in columns 3 and 6. These columns form a X-Wing pattern in rows 1 and 6.

Sudoku grid illustrating step 1: Finned X-Wing — Check digit 3 in columns 3 and 6. These columns form a X-Wing pattern in rows 1 and 6.

2

Finned X-Wing

r4c3 is already filled with 6.

Sudoku grid illustrating step 2: Finned X-Wing — r4c3 is already filled with 6.

3

Finned X-Wing

r5c3 is already filled with 1.

Sudoku grid illustrating step 3: Finned X-Wing — r5c3 is already filled with 1.

4

Finned X-Wing

Digit 3 cannot go in r7c3 because r7c8 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 4: Finned X-Wing — Digit 3 cannot go in r7c3 because r7c8 is already in this row. Remove the entry or choose a different digit.

5

Finned X-Wing

r8c3 is already filled with 4.

Sudoku grid illustrating step 5: Finned X-Wing — r8c3 is already filled with 4.

6

Finned X-Wing

r9c3 is already filled with 7.

Sudoku grid illustrating step 6: Finned X-Wing — r9c3 is already filled with 7.

7

Finned X-Wing

r2c6 is already filled with 1.

Sudoku grid illustrating step 7: Finned X-Wing — r2c6 is already filled with 1.

8

Finned X-Wing

r3c6 is already filled with 7.

Sudoku grid illustrating step 8: Finned X-Wing — r3c6 is already filled with 7.

9

Finned X-Wing

r4c6 is already filled with 9.

Sudoku grid illustrating step 9: Finned X-Wing — r4c6 is already filled with 9.

10

Finned X-Wing

Digit 3 cannot go in r5c6 because r5c7 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 10: Finned X-Wing — Digit 3 cannot go in r5c6 because r5c7 is already in this row. Remove the entry or choose a different digit.

11

Finned X-Wing

Digit 3 cannot go in r7c6 because r7c8 is in this row and r9c4 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 11: Finned X-Wing — Digit 3 cannot go in r7c6 because r7c8 is in this row and r9c4 is in this box. Remove the entry or choose a different digit.

12

Finned X-Wing

r8c6 is already filled with 2.

Sudoku grid illustrating step 12: Finned X-Wing — r8c6 is already filled with 2.

13

Finned X-Wing

r9c6 is already filled with 5.

Sudoku grid illustrating step 13: Finned X-Wing — r9c6 is already filled with 5.

14

Finned X-Wing

One base column has extra candidates in box 1. That box is the fin, so this becomes a Finned X-Wing.

Sudoku grid illustrating step 14: Finned X-Wing — One base column has extra candidates in box 1. That box is the fin, so this becomes a Finned X-Wing.

15

Finned X-Wing

Because of the fin, only cells in box 1 that also lie in rows 1 and 6 can lose digit 3.

Sudoku grid illustrating step 15: Finned X-Wing — Because of the fin, only cells in box 1 that also lie in rows 1 and 6 can lose digit 3.

16

Finned X-Wing

These are the cells that see both the fish structure and the fin: r1c2.

Sudoku grid illustrating step 16: Finned X-Wing — These are the cells that see both the fish structure and the fin: r1c2.

17

Finned X-Wing

Remove 3 from: r1c2.

Sudoku grid illustrating step 17: Finned X-Wing — Remove 3 from: r1c2.

18

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

The fin must be in the same block as one of the proper X-Wing cells.
Finned fish reduce the elimination zone but still allow some progress.
These appear when you almost have a perfect fish pattern.