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Nov 26 VH

 
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Wed Nov 25, 2009 10:59 pm    Post subject: Nov 26 VH Reply with quote

Clustered in the begining.
After basic reductions:triples and pairs an XY-Wing-<57>-<78>-<58> is revealed eliminating 5 in r4c8 solving the puzzle in one step.
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Marty R.



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

PostPosted: Thu Nov 26, 2009 5:49 am    Post subject: Reply with quote

There were a couple of XY-Wings that I saw. For those who enjoy alternatives:

Code:

+---------+--------+------------+
| 59 2  6 | 7 39 8 | 135 4  15  |
| 3  7  4 | 1 2  5 | 6   9  8   |
| 59 1  8 | 4 39 6 | 357 2  57  |
+---------+--------+------------+
| 2  9  1 | 6 8  4 | 57  57 3   |
| 6  4  3 | 2 5  7 | 18  18 9   |
| 8  5  7 | 9 1  3 | 2   6  4   |
+---------+--------+------------+
| 47 68 9 | 5 46 1 | 78  3  2   |
| 1  68 2 | 3 7  9 | 4   58 56  |
| 47 3  5 | 8 46 2 | 9   17 167 |
+---------+--------+------------+

Play this puzzle online at the Daily Sudoku site

There is a potential DP 59-39-35 in boxes 123. R1c7 must be = 1 or r3c7 must = 7 to break the pattern. If r1c7 =1, then r9c8 =7 and this and r3c7 act as pincers 7, removing the 7 from r7c7.
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arkietech



Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA

PostPosted: Thu Nov 26, 2009 2:16 pm    Post subject: Reply with quote

I ended up with a bug+1 putting a 7 in r9c9.
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roaa



Joined: 18 Apr 2009
Posts: 112
Location: Sweden

PostPosted: Thu Nov 26, 2009 3:14 pm    Post subject: Reply with quote

There are actually two xy-wings 578. The other eliminates 7 in r4c7.
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cgordon



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

PostPosted: Thu Nov 26, 2009 4:06 pm    Post subject: Reply with quote

Quote:
For those who enjoy alternatives:

For that reason - I used an APE (Aligned Pair Exclusion) in R89C8. (Hey - if you can't find anything unique - what's the point of posting!)
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Roger S



Joined: 20 Jun 2009
Posts: 6
Location: UK

PostPosted: Thu Nov 26, 2009 7:59 pm    Post subject: Nov 26 VH Reply with quote

Could you confirm if <17> <78><18> is a valid XY Wing eliminating the 8 in R5 C7.
Just trying to learn how to recognise them

Thanks

Roger
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Marty R.



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

PostPosted: Thu Nov 26, 2009 8:09 pm    Post subject: Reply with quote

Yes Roger, that is a valid XY-Wing. It also eliminates the 8 from r8c8, although that would get eliminated based on the elimination you mentioned. It's just that it's a good idea to look for all possible eliminations.
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Roger S



Joined: 20 Jun 2009
Posts: 6
Location: UK

PostPosted: Thu Nov 26, 2009 8:50 pm    Post subject: Reply with quote

Thanks Marty Understood
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