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It looks like type 3 is a special case of type 1 that doesn't offer anything different. Why are they distinguished from each other?

I guess because type 3 "looks" like type 2 (one elimination) but in fact has the same eliminations as type 1. But I agree, it's bizarre to have types 1 and 3 distinguished. --Nd 07:09, 8 January 2007 (CET)

I agree that Subtype 1 and 3 are exactly the same.

Even more, I think it is not necesary to include subtypes in XY-Wing. The formal definition is very clear, and can be assimilated to the definition of a "naked triple" with two conditions: The three cells must be two-candidate cells, in the form XY - YZ - ZX; and they are not in the same house, but one of them (the pivot) can see the other two (the pincers). Asuming XY is the pivot, and focusing on digit Z, you can eliminate this digit "Z" from all cells that can be simultaneously seen by both pincers. In my modest opinion, that's enough.

And in my opinion, real examples must be given in as much solving categories as possible; the diagrams are useful, but an example can clarify the idea more than a simple diagram.

Saludos.

I'm sorry for the addition of my sign in the main article... I forgot that that was not a discussion, but the main article!

Thank you for correcting the mistake. Pedro Argal.

I realize that logically types 1 and 2 are the same--eliminate all instances of candidate Z from cells that see both the XZ and YZ cells--but they should be distinguished because (at least for me) the visual difference between types 1 and 2 is important when scanning the grid. --Nd 06:02, 10 January 2007 (CET)

We all agree that all three "types" are logically the same, except with visual differences. How about calling these "illustrations" rather than "types", and removing the third one? --unkx80

I agree with your proposition. Pedro

The distinction into 3 types was proposed on the Players forum and other forums by Myth Jellies, to help developing players to recognize XY-Wings. It received good responses, so I decided to include the subtyping into the article.

There are at least two subtypes, the box-line (type 1) and the row-column (type 2). These are clearly different, because type 1 can eliminate upto 5 candidates and type 2 only a single candidate.

Type 3 is a combination, but has the same effect as type 1, so it can be omitted.

--Ruud 20:21, 10 January 2007 (CET)

In my opinion, it is OK now. Pedro Argal.