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Sept 8 VH

 
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cgordon



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

PostPosted: Sat Sep 08, 2007 12:18 pm    Post subject: Sept 8 VH Reply with quote

There are a couple of URs available.

UR for 267 leaves 38 in R2C3

UR for 247 leaves 1 in R5C8

I was left with a Bug+1 to solve.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sat Sep 08, 2007 1:10 pm    Post subject: Reply with quote

At the point of the BUG+1, there are also 2 XY-wings and 2 W-wings that solve it.
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS

PostPosted: Sat Sep 08, 2007 2:20 pm    Post subject: Sept 8 VH Reply with quote

I used a W-wing to eliminate 4 in R2C5 and the rest was singles.

Earl
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Sat Sep 08, 2007 10:16 pm    Post subject: Reply with quote

Two xy-wings with pivot in R4C1 and pivot in R2C2, was the final step for me, I missed the W-wing Earl and Tracy were refering to completely.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Sep 09, 2007 12:40 am    Post subject: Reply with quote

I don't recall seeing any W-Wings (which doesn't mean they weren't there) and didn't reach a BUG+1 position, but two XY-Wings solved the puzzle.
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eddieg



Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA

PostPosted: Mon Sep 10, 2007 10:47 pm    Post subject: Reply with quote

UR involving 3 Numbers per square.

I have never seen UR's with the 3 numbers as in this puzzle. Can somebody point me to something that describes UR's so I can read more about it ?

Thanks in Advance.
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cgordon



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

PostPosted: Mon Sep 10, 2007 11:48 pm    Post subject: Reply with quote

I printed out a very useful explanation for URs from Keith's post:
http://www.sudoku.com/boards/viewtopic.php?p=29105#29105

I can't see why a Type 1 should not work the same if you add one or even more identical numbers to all 4 corners.

I like URs - I think they are easy to spot. In fact I brilliantly used a Type 4 to solve Sept 1 VH. At least I think I did.
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Asellus



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

PostPosted: Tue Sep 11, 2007 12:01 am    Post subject: Reply with quote

I have pondered it and I can't see how the 3-digit UR eliminations posted by cgordon are legitimate. Generally, the 3-digit (4-cell) pattern does not seem so helpful with UR logic as far as I can tell. Perhaps someone else can provide the supporting logic.

Here's the grid I believe we are considering:
Code:
+----------------+-----------+-------------+
| 5    1   36    | 7  2  36  | 8   9    4  |
| 3467 468 23678 | 1  34 9   | 5   267  27 |
| 467  9   267   | 5  8  46  | 1   267  3  |
+----------------+-----------+-------------+
| 14   2   9     | 6  7  8   | 34  134  5  |
| 8    5   17    | 9  34 234 | 247 1247 6  |
| 3467 46  367   | 24 1  5   | 9   8    27 |
+----------------+-----------+-------------+
| 9    7   5     | 24 6  1   | 234 234  8  |
| 16   68  168   | 3  5  24  | 247 247  9  |
| 2    3   4     | 8  9  7   | 6   5    1  |
+----------------+-----------+-------------+

The 247 case is R58C78. I can't see any eliminations that are supported by UR logic in this case.

The 267 case is R23C38. In this case, there is a possible UR-based elimination: <6> can be removed from R3C3. It depends on the <2> strong link in R23C3 and the 27 bivalue at R2C9. If R3C3 is <2>, it isn't <6>. If, alternately, R2C3 is <2>, the R23C8 becomes {26} due to the bivalue and R3C3 also cannot be <6>, to avoid the UR.

More than that, I cannot see.
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cgordon



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

PostPosted: Tue Sep 11, 2007 11:36 am    Post subject: Reply with quote

Yeah: I think I made a false assumption. The UR says if you have a 12 in three corners and a 123 in the fourth - - then the 123 becomes a 3. I asumed that if you had a 123 in three corners and a 1234 in the fourth - the 123s would cancel out leaving the 4. But thinking about it the UR can only work if there are two choices for two corners.

Problem is, it's worked on at least 3 occassions. Maybe a probability thing - or just l got lucky. Sorry about error.
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DennyOR



Joined: 12 Sep 2007
Posts: 33
Location: Portland, Oregon

PostPosted: Wed Sep 12, 2007 7:39 pm    Post subject: Reply with quote

A 4s skyscraper in cols 2 and 5 goes a long way toward the solution from the position posted by Asellus.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Wed Sep 12, 2007 9:20 pm    Post subject: Reply with quote

But not all the way...
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Wed Sep 12, 2007 11:00 pm    Post subject: Reply with quote

TKiel wrote:
But not all the way...

Or, from Asellus' position, an XY-wing, then another.

Keith
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