Why Isn’t this an x-wing? Or is it?

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Why Isn’t this an x-wing? Or is it?

Postby fdh319 » Thu Dec 01, 2016 10:15 am

I’ve searched the web for x-wings and all the examples are of the type: r26c48, r59c58, r37c28 and so on. That is, no pattern can be found in the same band or stack. But what about a shape like this r46c19?
Why_not_x-wing.PNG
Why_not_x-wing.PNG (22.23 KiB) Viewed 169 times

Its four end points of candidate 6 are all in the same middle band (in blue). Since it’s in columns, it eliminates candidate 6 in rows four and six (in yellow) and places a 6 in the pink cell r5c5. How do you call a pattern like this if not a legitimate x-wing?
Here’s another example of candidate 9 in the upper band r23c58 also in columns:
Why_not_x-Wing2.PNG
Why_not_x-Wing2.PNG (18.25 KiB) Viewed 169 times

This time it eliminates all other 9’ns in boxes two and three using “the locked candidate type 2” method. But the eliminated r2c3 is clearly the result of an x-wing. Isn’t it?
BTW, although both examples of the suspected x-wings are in bands I’ve seen a lot of them also in stacks.
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Re: Why Isn’t this an x-wing? Or is it?

Postby champagne » Thu Dec 01, 2016 11:08 am

likely because in such cases it's not the easiest move.

In your first example; 6r5c5 is a hidden single in row five
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Re: Why Isn’t this an x-wing? Or is it?

Postby JasonLion » Thu Dec 01, 2016 2:38 pm

Your first example is an X-Wing. However, the same eliminations can be made with a simpler move, naked single, so no one would normally mention the X-Wing.

You second example is likewise an X-Wing. This time it takes three simpler techniques to cause all the same eliminations: locked candidates twice and naked single once. Again, the simpler techniques dominate, so the X-Wing would not normally be mentioned.

Solving techniques are not normally considered unless all basic moves have been made first. In the case of X-Wing this doesn't really make any difference, but some of the more complex techniques depend on basics having been completed, so that has become the standard.
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Re: Why Isn’t this an x-wing? Or is it?

Postby fdh319 » Fri Dec 02, 2016 8:08 am

Agreed. But not mentioning an x-wing does not mean that it does not exist. And then what about instances where I see such an x-wing first, before a hidden single, or locked candidate and such? :)
Now, I’m about to tell you guys that shortly after sending this post, after all, I discovered an alternative name for the x-wing like configuration. It appears in the 6th grid from the top here:

https://www.geocaching.com/geocache/GC33KDE_intermediate-sudoku-strategies-ghost-numbers

The author of that site calls it a mini x-wing! Maybe this name suits better and should be adopted by the Sudoku community. Here’s what he says: “ Some commentators call this position a "Mini X-Wing" based on its similarity to a real X-Wing. If you can wrap your head around this position, it may help you better visualize X-Wings”.
Next, to my dismay I found a mistake in my presentation of the second grid above. It should be: after the locked candidate type 2 method is applied, a mini x-wing is established and not the other way around.
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Re: Why Isn’t this an x-wing? Or is it?

Postby JasonLion » Fri Dec 02, 2016 1:57 pm

The name debate happened long ago, and is already firmly decided in favor of X-Wing. I doubt that you will find any support for reopening that discussion. Also, the source you quote is more recent than the naming of the technique, and not considered authoritative. The story about being named after the Star Wars fictional space ship is generally accepted as true, just without the "mini".

Patterns that disappear when you apply basics are not generally considered valid examples of a technique. In this case the logic still works so there is no harm in using them if you see them. Calling that an X-Wing when notating a solution would be only mildly controversial. Providing that as an example when defining the technique would probably not be accepted.
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Re: Why Isn’t this an x-wing? Or is it?

Postby fdh319 » Sat Dec 03, 2016 12:46 pm

Thanks for clarifying this matter. Originally I asked if such patterns in bands or in stacks go under the name of x-wings or not. So if the answer is positive, I’m more than happy.
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