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X-Wings, swordfish, etc.

 
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Marty R.



Joined: 12 Feb 2006
Posts: 5181
Location: Rochester, NY, USA

PostPosted: Wed Mar 22, 2006 5:56 pm    Post subject: X-Wings, swordfish, etc. Reply with quote

If one goes down each row nine times (once for each number), notes which columns contain that number and finds no X-Wings, swordfish, etc., is it still possible to find them by checking each column to see what rows contain the number?
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Wed Mar 22, 2006 11:05 pm    Post subject: X-Wings, swordfish, etc. Reply with quote

No. If there is, say, an X-wing based on columns for a particular candidate, the dual fish that you turn up on the rows will make the same eliminations.

Steve
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Thu Mar 23, 2006 1:25 am    Post subject: Reply with quote

If an X-wing occurs in both rows and columns, it is not useful. (For then each candidate occurs only twice in each row and column, and there are no possibilities to eliminate.)

Marty,

To answer your basic question, you must look in both rows and columns. Separately.

The key to these fishes is that they are built on possibilities that occur only twice in a row or column. What I do is to make notations outside the puzzle (next to each row and column) of which possibilities occur only twice.

Then, I look at them to see if they line up to make fishes or coloring chains. (An X-wing is very often also a U- or C-shaped coloring chain connecting four squares.)

Best wishes,

Keith
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Thu Mar 23, 2006 3:59 am    Post subject: Reply with quote

Keith

I understood Marty to be considering fish of all sizes. No one has suggested that the dual of an X-wing on rows is an X-wing on columns. In general it is not. For example, the dual of an X-wing may be a jellyfish.

Steve
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Thu Mar 23, 2006 3:05 pm    Post subject: Small fry are easier to catch Reply with quote

Steve R wrote:
I understood Marty to be considering fish of all sizes. No one has suggested that the dual of an X-wing on rows is an X-wing on columns. In general it is not. For example, the dual of an X-wing may be a jellyfish.

I think Keith understands that. All he's trying to suggest is that it's usually easier to spot an X-Wing pattern (4 cells) than it is to find a swordfish (up to 9 cells), or a jellyfish (up to 16 cells). Squirmbags? Those can contain up to 25 cells -- good luck findng one of those, even if you know that it's there.

I've spotted a couple of "jellyfish" in puzzles and felt pretty good about it, too ... until I realized that if I had just rotated my attention by pi/2 I would have found an X-Wing! dcb
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Marty R.



Joined: 12 Feb 2006
Posts: 5181
Location: Rochester, NY, USA

PostPosted: Thu Mar 23, 2006 5:55 pm    Post subject: Reply with quote

As always, thanks for the helpful replies.
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Thu Mar 23, 2006 11:59 pm    Post subject: Reply with quote

Actually, at the time, I misunderstood Steve R's point. My statement (while correct) is an inappropriate response.

Sorry for that.

(Also, it had to happen on my 100th post!)

Keith
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