## Invalid Vertical Swordfish

Post the puzzle or solving technique that's causing you trouble and someone will help

### Invalid Vertical Swordfish

Is there such a thing as an invalid vertical swordfish? I was working on a puzzle and I thought I had established a swordfish of 7's, but the application of the swordfish method produced an invalid result.

The initial grid looks like this:

A2=2
A8=7
B4=5
B6=8
B9=4
D1=4
D5=3
D9=8
E2=7
E5=9
E8=2
F1=6
F5=1
F9=5
H1=5
H4=6
H6=4
H9=1
I2=3
I8=9

As you solve the puzzle, you will see that a vertical swordfish of 7's looks like it could be established at C4, D4, I4; C6, F6, I6; D7, F7. However, when you remove the 7's from C1, I1 and I9, you will notice two things: (1) removing the 7's from C1 and I1 makes G1 the only 7 remaining in Column 1. When you set G1 at 7, and remove the 7 from G9, column nine no longer has a cell for value 7.

If you have any insights into this issue, I would sure like to hear them.

Posts: 2
Joined: 12 January 2006

it would be easier to follow if you'd posted the grid in a more useable format - check what others have done when they're asking for assistance. I might get to this one a bit later when I have more time, but someone else will probably beat me to it. I suspect you may be overlooking a hidden single or at least be able to place one of the 7s before you resort to a swordfish, but without doing up the grid properly it's just a guess.
Shazbot

Posts: 220
Joined: 24 September 2005

### Re: Invalid Vertical Swordfish

Paladin wrote:C4, D4, I4; C6, F6, I6; D7, F7

I must confess that I haven't reconstructed the puzzle to get a clearer image. It would help more if you would post the actual grid.

It seems that the cells you chose fall into 3 columns (4,6,7) & 4 rows (C,D,F,I) that does not constitute a swordfish.

tarek

Posts: 2851
Joined: 05 January 2006

Here is the Grid assuming A, B, C are Rows and 1, 2, 3 are columns, if not it is still the same puzzle but with rows as columns and columns as rows.
There was a thread to the terms used in this forum (Row, column, band, stack, chute etc) from pappocom but that seems to be lost to the Peruvian Security Team that hacked into the site, maybe someone in this forum will post a new Sticky 'Basic Terms' Thread.

Code: Select all
` . 2 . | . . . | . 7 .  . . . | 5 . 8 | . . 4  . . . | . . . | . . . -------+-------+------  4 . . | . 3 . | . . 8  . 7 . | . 9 . | . 2 .  6 . . | . 1 . | . . 5 -------+-------+------  . . . | . . . | . . .  5 . . | 6 . 4 | . . 1  . 3 . | . . . | . 9 . `
Crazy Girl

Posts: 189
Joined: 08 November 2005

Regardless of the specifics, no, it's impossible to have an invalid Swordfish. If you end up in a invalid position, you either made an exclusion where you shouldn't have or placed a number where it doesn't belong -- either before, after or during using the Swordfish.

(Thanks Crazy girl for making the grid and congratulations to Paladin
for most annoy way to post a puzzle.)

See: http://forum.enjoysudoku.com/viewtopic.php?t=2664

I didn't find I needed a swordfish in 7s to solve -- though I did find two others, in 1s and in 3s. I did find an x-wing in 7s -- maybe you combined it with a third row/column and mistook it for a swordfish? A common mistake in identifying a swordfish is not realizing that you are using 4 rows or columns instead of 3.
tso

Posts: 798
Joined: 22 June 2005

Your points do not form a swordfish. You have 4 rows (C, D, F, I) and 3 columns (4, 6, 7), or vice versa. You need to have an equal number of columns and rows for X-wings/Seafood.
Myth Jellies

Posts: 593
Joined: 19 September 2005

### Invalid Vertical Swordfish

Thank you, Tarek and Myth Jellies, for your response. I did not notice that my "swordfish" included four rows. I sometimes suffer from spatial disorientation when I work on these puzzles.

I am sorry I did not present my start grid in an appropriate format. I don't know how to create these grids, but I did do the best I could with my limited skills.