Finned X-Wing

This is an example of a standard X-Wing.

We have two columns with Strong Links between the '6' candidates, where the '6' candidates are also in the same row for both columns.

This allows us to remove all other '6' candidates in the 2 rows.

A Finned X-Wing relaxes the requirements a little, but we can't remove as many candidates.

This situation is almost an X-Wing on the 6 candidates in rows 6 and 9.

Row 9 has only two 6 candidates.

However, row 6 has an extra cell containing the 6 candidate - without this extra candidate, this situation would be a vanilla X-Wing.

Despite not being quite an X-Wing, we can still make progress here.

There are four options for the placement of 6 in rows 6 and 9.

This is option 1.

Option 2.

Option 3.

Option 4.

Looking at the four options, we know that (at least) one of the cells labelled A, B and C will contain a 6.

This allows us to remove the '6' candidates from the cells highlighted in red.

(From a terminology poing of view, the red cells can 'see' cells A, B and C).

This is another example of a Finned X-Wing.

We almost have an X-Wing on the '8' candidate in rows 6 and 8, but we have an extra cell/'fin' in row 8.

We can still remove any '8' candidates that are in the same column as the X-wing AND in the same region as the extra 'fin' cell.

This is a column-oriented Finned X-Wing.

We have the base X-Wing across columns 2 and 6 with rows 3 and 6, with an extra fin in column 6.

This allows us to remove the '1' candidates that see both the base X-Wing cell and the extra fin cell.

You will sometimes see a situation where you have 2 fin cells - they have to be in the same region.

The same reasoning applies, we can remove all candidates that can see the base X-Wing cell and the extra fin cell.

When looking at situations where you might be able to apply the Finned X-Wing technique, you are looking for,

A standard X-Wing with one or more fin cells.
The fin cells have to be in the same region as each other and one of the vanilla X-Wing cells.
Removing all of the fin cells would leave a standard X-Wing.

This allows us to remove candidates in cells that can see the fin cells and the associated standard X-Wing cell.

Can you spot the Finned X-Wing here?

Did you spot it?

Can you spot the Finned X-Wing here?

Did you spot it?

It's also possible with a Finned X-Wing that one of the cells will be filled in with a value.

We can still apply the Finned X-Wing technique here.

But, the filled cell has to be in the same region as the fin cell(s), it doesn't work if any other cell is filled.

This variation on a Finned X-Wing is known as a Sashimi X-Wing.

Here is another Sashimi X-Wing.

Can you spot the Sashimi X-Wing in this grid?

Did you spot it?

Practice puzzles

Here are 22 Sudoku puzzles in total. The first 10 require you to apply Finned X-Wing (and no other techniques), the second set of 10 require Sashimi X-Wing, the last 2 are bonus grids.

Sudoku Academy

X-Wing

Finned X-Wing

Practice puzzles