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Dec 15 vh
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Sat Dec 15, 2007 1:40 pm    Post subject: Dec 15 vh Reply with quote

One single xy-wing.
Doesn't seem to do much (removes 3 out of a cell with 5! candidates {3,4,7,8,9}).

But it solves the puzzle.

Better fill in your PMs, guys....


Hm ... Is that a semi-O-wing then?

_______

For you friends of w-wings out there:
(8)r1c8= [83-35-57-76-63-38] =(8)r9c7; removes a LOT of "8"s in r7c8 r1c7 r2c7 r3c7.
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keith



Joined: 19 Sep 2005
Posts: 3315
Location: near Detroit, Michigan, USA

PostPosted: Sat Dec 15, 2007 2:51 pm    Post subject: Reply with quote

There are two UR's, but they don't solve the puzzle. Here is the grid after basics:
Code:
+-------------------+-------------------+-------------------+
| 89    4     35%   | 6     5789  1     | 3789  38@   2     |
| 2     7     6     | 4     589   3     | 89    1     59    |
| 89    3-5   1     | 2     5789  79    | 34789 6     459   |
+-------------------+-------------------+-------------------+
| 7     29    29    | 3     4     6     | 1     5     8     |
| 5     1     4     | 8     79    79    | 6     2     3     |
| 3     6     8     | 1     2     5     | 49    7     49    |
+-------------------+-------------------+-------------------+
| 6     89    79    | 5     13    4     | 2     38#   17    |
| 4     23    23    | 7     16    8     | 5     9     16    |
| 1     58%   -57   | 9     36    2     | 38@   4     67    |
+-------------------+-------------------+-------------------+

I do not see that the cells @, R1C8 and R9C7 are a W-wing. They are linked through the pair <38> # in R7C8. All you can say is that R1C8 and R9C7 have the same value. They are either both <3>, or both are <8>.

But, they are very useful! Take a look at R1 and R9. There is an extended XY-wing: <35> <38> <38> <38> <58>, %-@-#-@-% which takes out <5> in R3C2 and R9C3, solving the puzzle.

Keith


Last edited by keith on Sat Dec 15, 2007 3:23 pm; edited 1 time in total
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sat Dec 15, 2007 3:17 pm    Post subject: Reply with quote

keith and nataraj,

You are both right. It is a W-Wing via that XY Chain: one or both must be <8>. And, via the single {38} bivalue, both must be <3> or both must be <8>. The only option that satisfies both demands is: both must be <8>, which is indeed the case.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sat Dec 15, 2007 3:26 pm    Post subject: Reply with quote

I used a UR <79> R35 to leave <58> in R3C5
then a <589> xy-wing; pivot <89> in R2C7 that removed <5> in R2C5
then another UR <49> in C79
then a <358> xy-wing; pivot <58> R9C2 that removed <3> from R3C7

Sure - it could have been done in one step - but I had fun !!

BTW. I am very pleased to see something like 6 VHs in the last 10 days. Thank you. That's the way it should be. Let the plebs get their easy puzzles in the tabloids and leave this Forum to the sophisticates like what we are.
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Marty R.



Joined: 12 Feb 2006
Posts: 5732
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PostPosted: Sat Dec 15, 2007 3:28 pm    Post subject: Reply with quote

Quote:
Take a look at R1 and R9. There is an extended XY-wing: <35> <38> <38> <38> <58>, %-@-#-@-% which takes out <5> in R3C2 and R9C3, solving the puzzle.


Same solution here.
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keith



Joined: 19 Sep 2005
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PostPosted: Sat Dec 15, 2007 3:34 pm    Post subject: Reply with quote

Asellus wrote:
keith and nataraj,

You are both right. It is a W-Wing via that XY Chain: one or both must be <8>. And, via the single {38} bivalue, both must be <3> or both must be <8>. The only option that satisfies both demands is: both must be <8>, which is indeed the case.

Asellus,

Thank you. I am inclined not to call it a W-wing which, in my mind, is usually a three-link chain WX-X=X-WX with pincers W.

Nataraj,

I apologize that I more or less missed your point.

Keith
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Sat Dec 15, 2007 4:10 pm    Post subject: Reply with quote

no problem, keith. And thanks, Asellus for your explanation. I can see that the "shorthand" notation for my xy-chain was too confusing. I was just too lazy to note all the steps in the chain with r1c3 ...

And to avoid any other misunderstanding: my xy-wing was 35-58-38 with pivot r9c2. It tkes out the "3" in r3c7 which makes 3 in r3c2 a hidden single.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Sat Dec 15, 2007 8:02 pm    Post subject: Reply with quote

cgordon wrote:
... and leave this Forum to the sophisticates like what we are.


Are you being serious, cgordon, or just the tiniest bit trolling ?


____


edit. I checked. The last time anybody posted in this forum about a NOT vh puzzle was on Oct 30 by one "cgordon" Laughing

Quote:
BTW. I am very pleased to see something like 6 VHs in the last 10 days. Thank you.
I couldn't agree more.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sat Dec 15, 2007 8:26 pm    Post subject: Reply with quote

Quote:
The last time anybody posted in this forum about a NOT vh puzzle was on Oct 30 by one "cgordon"


That's when I was a neophyte and a philistine.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Sat Dec 15, 2007 8:40 pm    Post subject: Reply with quote

cgordon wrote:
Quote:
The last time anybody posted in this forum about a NOT vh puzzle was on Oct 30 by one "cgordon"


That's when I was a neophyte and a philistine.


... and so much younger...
Smile glad to hear that.

___

P.S. nothing better than a little provocation to liven things up once in a while
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Marty R.



Joined: 12 Feb 2006
Posts: 5732
Location: Rochester, NY, USA

PostPosted: Sat Dec 15, 2007 10:17 pm    Post subject: Reply with quote

cgordon wrote:
Quote:
The last time anybody posted in this forum about a NOT vh puzzle was on Oct 30 by one "cgordon"


That's when I was a neophyte and a philistine.


From neophyte and philistine to sophisticate in a mere 45 days redefines the term "warp speed." Wink
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mckeann



Joined: 29 Nov 2007
Posts: 4

PostPosted: Sat Dec 15, 2007 11:43 pm    Post subject: Reply with quote

All the explanations make sense, but i'm damned if i can spot the pattern without a clue from here Sad
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Marty R.



Joined: 12 Feb 2006
Posts: 5732
Location: Rochester, NY, USA

PostPosted: Sun Dec 16, 2007 12:56 am    Post subject: Reply with quote

mckeann wrote:
All the explanations make sense, but i'm damned if i can spot the pattern without a clue from here Sad

Neil,

There are multiple techniques discussed here. Is there one in particular for which you're having difficulty spotting the pattern?
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sun Dec 16, 2007 12:58 am    Post subject: Reply with quote

geez, if i would have read the forum first I would have not gone through two ur's and some coloring only to find out that it has one step.

so this puzzle had a one "major" step life expectancy.

been a few VH's that didn't have a very long life expectancy.
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mckeann



Joined: 29 Nov 2007
Posts: 4

PostPosted: Sun Dec 16, 2007 1:11 am    Post subject: Reply with quote

Marty R. wrote:
mckeann wrote:
All the explanations make sense, but i'm damned if i can spot the pattern without a clue from here Sad

Neil,

There are multiple techniques discussed here. Is there one in particular for which you're having difficulty spotting the pattern?



the pattern spotted by keith in the second post. I have all the same info, just cant seem to spot that they all line up.
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Marty R.



Joined: 12 Feb 2006
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PostPosted: Sun Dec 16, 2007 4:52 am    Post subject: Reply with quote

Quote:
the pattern spotted by keith in the second post. I have all the same info, just cant seem to spot that they all line up.


He talked about a couple of things. I can talk about the XY-Wing. I assume you're familiar with them. It's the pivot 58 in r9c2 and the pincers in r3c2 and r9c7. These pincers take out only a 3 from r3c7. But if r9c7 is 3, then r7c8 must be 8 and r1c8 must be 3. That becomes a new pincer which, working with the original pincer in r3c2, takes out the 3 from r1c3 and that solves the puzzle.
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nataraj



Joined: 03 Aug 2007
Posts: 1047
Location: near Vienna, Austria

PostPosted: Sun Dec 16, 2007 11:27 am    Post subject: Reply with quote

Marty R. wrote:
These pincers take out only a 3 from r3c7. But ...


Just for the record... Once 3 is gone from r3c7, r3c2=3 (single in r3), r1c3=5 (single) , r9c3=7 (single), and so on. No need for pincers.

I think what keith was getting at with his diagram ...
Quote:
the pattern spotted by keith in the second post. I have all the same info, just cant seem to spot that they all line up.

... was the "extended xy-wing".

This is how they "line up":

if r1c3 (marked %) =5 then r3c2<>5.
if r1c3 <> 5 (but is 3), then (the chain marked @#@ is set in motion and) r1c8=8, r7c8=3, r9c7=8, and finally r9c2=5. This again makes r3c2<>5

Of course, in the end it makes no difference whether one takes out the 3 in r1c3 first or the 5 in r3c2, the puzzle is solved either way.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Dec 16, 2007 11:43 am    Post subject: Reply with quote

mckeann,

Perhaps you are referring to Keith's "extended XY Wing," which is actually a particular instance of an XY Chain, that removes the two <5>s. It involves the following cells in sequence:
r1c3 - r1c8 - r7c8 - r9c7 - r9c2
And, it works in this way:
(1) If r1c3 is <5>, then r3c2 and r9c3 cannot be <5>. (And we have no idea what r9c2 is.)
(2) If r1c3 is NOT <5>, then it is <3> and r1c8 is <8> and r7c8 is <3> and r9c7 is <8> and r9c2 is <5>... and r3c2 and r9c3 cannot be <5>.
So, since either (1) or (2) must be true, then one or both of r1c3 and r9c2 must be <5> and r3c2 and r9c3 can never be <5>.

A similar XY Wing would have a {35} - {38} - {58} structure. Because two more {38} cells occur in the middle, Keith called it an "extended" XY Wing.

[Edit: nataraj's post wasn't there when I started this. Well, two heads are better than one!]
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keith



Joined: 19 Sep 2005
Posts: 3315
Location: near Detroit, Michigan, USA

PostPosted: Sun Dec 16, 2007 12:35 pm    Post subject: Reply with quote

I think Neil is complaining that he sees the cells, but does not recognize the pattern.

Any time you have three cells with the same pair of candidates that form two strong links, you should look for opportunities. The chain fragment is

XY=XY=XY

and, in the solution, each end has the same value, X or Y.

In this case, Marty and I used it to extend an XY-wing. The regular XY-wing is

XZ-XY-YZ

with pincers Z. (Any cell that sees both ends cannot be Z.) The extended wing is

XZ-XY=XY=XY-YZ

and has the same pincers, Z.

You can also possibly extend the end of an XY-wing:

XZ-XY-YZ=YZ=YZ

Another possibility is a step in Medusa coloring. Is there a strong link in either X or Y on one end? For example,

X=XY=XY=XY

is a chain that has X as pincers.

[Edit: Actually, this last one is simple coloring on X. The Medusa chain is

X=XY=Y=XY

and has X as pincers.]

Keith


Last edited by keith on Sun Dec 16, 2007 5:41 pm; edited 1 time in total
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Marty R.



Joined: 12 Feb 2006
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PostPosted: Sun Dec 16, 2007 4:51 pm    Post subject: Reply with quote

Quote:
Just for the record... Once 3 is gone from r3c7, r3c2=3 (single in r3), r1c3=5 (single) , r9c3=7 (single), and so on. No need for pincers.


Clearly, I missed that. But it's fun to do pincer coloring since it's relatively new to me. Wink
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