dailysudoku.com

JV · Joined: 09 Jan 2011 Posts: 24 Location: Devon, England

Menneske 2170801

daj95376 · Joined: 23 Aug 2008 Posts: 3854

Every puzzle should have a solution. I don't know about JV's "magic bullet", but ...

I don't recall my solver's network logic previously leading me to a 5-cell ALS.

tlanglet · Posted: Sun Feb 27, 2011 6:12 pm Post subject:

What a move Exclamation

I really doubt that a person would ever search for such an als but life is always got a surprise for us.

Ted

peterj · Joined: 26 Mar 2010 Posts: 974 Location: London, UK

Danny, nice!
I don't understand why you need to worry about r8c9?

Some might see it easier from the other angle...

daj95376 · Joined: 23 Aug 2008 Posts: 3854

JV · Joined: 09 Jan 2011 Posts: 24 Location: Devon, England

Thanks Danny & Peter. Amazing Eurekas! By 'magic bullet' I did indeed mean deleting the 5 in r3c9.

I don't know how other folk see things: I mean do you think in Eureka? (I do for an ordinary chain, but something like this is too complex for me.) I simply saw, as you no doubt did, that r8c9 = 4 => r7c1 = 4 => r8c1 = 1 => r3c1 = 5 => r3c9 <> 5.

Another test if you'd like one, how one expresses an APE in EUreka: there's one in r78c7. (I'd already removed the 7s in r47c7 because of the UR 78, but I don't think that makes any difference.)

peterj · Joined: 26 Mar 2010 Posts: 974 Location: London, UK

JV, I have never spent the time to get to grips with APE. Partly because I never see anyone use them (other than some computer solvers) and my understanding is that they can usually be represented by xyz+-wings and als-xz techniques...

There is an wxyz-wing (I think)... which is hard to represent in Eureka other than a kraken presentation...

Marty R. · Posted: Sun Feb 27, 2011 10:20 pm Post subject:

Peter, three years ago we started discussing APE here and this post by Keith probably put an end to it:

"All,

I did a search on APE, and was surprised to find my footsteps all over the discussion.

http://www.sudoku.com/boards/viewtopic.php?t=3882

As I now recall, Ruud proposed that APE was a missing method from the usual arsenal.

I did an analysis that showed APE is another (less general) form of XY, XYZ, and WXYZ-wings. In other words, APE makes one exclusion at a time, XY.. wings make multiple exclusions.

APE is a monkey that you should not worry about.

I welcome any example of an APE exclusion that is not an XY... wing.

Keith"

JV · Joined: 09 Jan 2011 Posts: 24 Location: Devon, England

Thanks Peter, but I think I'm sorry I asked!
Right-hand boxes with 7s gone (because of the UR78):

keith · Posted: Sun Feb 27, 2011 10:50 pm Post subject:

Here is the corrected link:

http://forum.enjoysudoku.com/aligned-pair-exclusion-ape-no-dj-t3882.html

Keith

JV · Joined: 09 Jan 2011 Posts: 24 Location: Devon, England

Marty, I've just read your post. I'm sure you're right, that APEs are a subset of more general methods. (And as I've said they're probably not common.) But . . . they're easy for some of us to spot where more complex methods might not be.

Isn't it the case with many common methods that they're special cases, used because they're easy to find? We like skyscrapers, but they're just one special type of single digit chain. Or W-wings, or whatever.

In this puzzle I was scratching round for something to do. I saw the APE simply because I find them fairly easy to see. I don't have the ability to see in any other way the two deletions I made.

JV · Joined: 09 Jan 2011 Posts: 24 Location: Devon, England

Now I've read Keith's post, including the link to the APE discussion, but that hasn't left me much wiser. I can see vaguely that the deletions I made are essentially because of an intersection of ALS in c7 and box 9. And if I were pressed I just might be able to formulate that. But so what? - I'd never have been able to see this in any other way.

keith · Posted: Sun Feb 27, 2011 11:17 pm Post subject:

keith · Posted: Mon Feb 28, 2011 2:42 am Post subject:

I have started an APE thread in the "Solving Techniques" forum. Please post further discussion and examples of Aligned Pair Exclusions there.

Keith

Asellus · Posted: Mon Feb 28, 2011 3:20 am Post subject:

JV · Joined: 09 Jan 2011 Posts: 24 Location: Devon, England

Thanks Asellus.

Keith, I do see that it's not necessary to use an APE, but that's how I saw it. If you write down the possible pairs for r78c7 you'll find that none of them includes a 2 or a 4 in r78c7, thus deleting them.

And I have to admit that Asellus is right, that it's not too diffcult to spot once you know to look. I suppose the question is how to know where to look for something.

tlanglet · Posted: Mon Feb 28, 2011 2:34 pm Post subject:

Asellus,

Once again you have pointed out another insight into the sudoku world. I, for one, have not considered the simple, obvious perspective for spotting an ALS that you presented.

Thanks...........

Ted