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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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 Posted: Sat Sep 08, 2007 12:18 pm Post subject: Sept 8 VH |
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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
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| Posted: Sat Sep 08, 2007 1:10 pm Post subject: |
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| 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
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| Posted: Sat Sep 08, 2007 2:20 pm Post subject: Sept 8 VH |
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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
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| Posted: Sat Sep 08, 2007 10:16 pm Post subject: |
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| 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
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| Posted: Sun Sep 09, 2007 12:40 am Post subject: |
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| 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
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| Posted: Mon Sep 10, 2007 10:47 pm Post subject: |
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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
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| Posted: Mon Sep 10, 2007 11:48 pm Post subject: |
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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
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| Posted: Tue Sep 11, 2007 12:01 am Post subject: |
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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
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| Posted: Tue Sep 11, 2007 11:36 am Post subject: |
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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
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| Posted: Wed Sep 12, 2007 7:39 pm Post subject: |
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| 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
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| Posted: Wed Sep 12, 2007 9:20 pm Post subject: |
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| But not all the way... |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Wed Sep 12, 2007 11:00 pm Post subject: |
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| TKiel wrote: | | But not all the way... |
Or, from Asellus' position, an XY-wing, then another.
Keith |
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