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Marty R. · Posted: Wed Mar 22, 2006 5:56 pm Post subject: X-Wings, swordfish, etc.

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?

Steve R · Posted: Wed Mar 22, 2006 11:05 pm Post subject: X-Wings, swordfish, etc.

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

keith · Posted: Thu Mar 23, 2006 1:25 am Post subject:

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

Steve R · Posted: Thu Mar 23, 2006 3:59 am Post subject:

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

David Bryant · Joined: 29 Jul 2005 Posts: 559 Location: Denver, Colorado

Marty R. · Posted: Thu Mar 23, 2006 5:55 pm Post subject:

As always, thanks for the helpful replies.

keith · Posted: Thu Mar 23, 2006 11:59 pm Post subject:

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