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May 30 VH

 
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roaa



Joined: 18 Apr 2009
Posts: 112
Location: Sweden

PostPosted: Sat May 30, 2015 9:10 am    Post subject: May 30 VH Reply with quote

I used two X-wings: One 237 gives r6c8<>2, which opens the second 789 giving r5c6<>9.
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dongrave



Joined: 06 Mar 2014
Posts: 326

PostPosted: Sat May 30, 2015 1:47 pm    Post subject: Reply with quote

Code:

 +----------------+----------------+----------------+
 | 9    6    37   | 8    1    27   | 4    23   5    |
 | 37   1    4    | 67   5    267  | 238  238  9    |
 | 5    2    8    | 9    3    4    | 1    6    7    |
 +----------------+----------------+----------------+
 | 6    9    23   | 4    7    38   | 28   5    1    |
 | 37   8    5    | 1    2    39   | 79   4    6    |
 | 1    4    27   | 5    6    89   | 2789 278  3    |
 +----------------+----------------+----------------+
 | 8    3    9    | 67   4    5    | 67   1    2    |
 | 2    57   1    | 3    8    67   | 567  9    4    |
 | 4    57   6    | 2    9    1    | 357  37   8    |
 +----------------+----------------+----------------+


I see a few different ways to solve it using two steps but I didn't see any one-steppers. Roaa's two XY-wings solves it - or his 1st XY followed by the a 278 XY - or you can start with the 278 XYZ followed by the 237 XY - but they all require two steps. Anyone out there use just one step?
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JC Van Hay



Joined: 13 Jun 2010
Posts: 494
Location: Charleroi, Belgium

PostPosted: Sat May 30, 2015 2:49 pm    Post subject: Reply with quote

Code:
+--------------+------------+----------------+
| 9   6   7-3  | 8   1  27  | 4     (23)   5 |
| 37  1   4    | 67  5  267 | 238   238    9 |
| 5   2   8    | 9   3  4   | 1     6      7 |
+--------------+------------+----------------+
| 6   9   (23) | 4   7  38  | (28)  5      1 |
| 37  8   5    | 1   2  39  | 79    4      6 |
| 1   4   (27) | 5   6  89  | 2789  (278)  3 |
+--------------+------------+----------------+
| 8   3   9    | 67  4  5   | 67    1      2 |
| 2   57  1    | 3   8  67  | 567   9      4 |
| 4   57  6    | 2   9  1   | 357   37     8 |
+--------------+------------+----------------+
[(3=2)r1c8 - 2r6c8=XYWing(278)r6c38,r4c7 - (2=3)r4c3] - (3=7)r1c3; stte
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rmireland



Joined: 21 Sep 2013
Posts: 33
Location: New Orleans

PostPosted: Sat May 30, 2015 4:25 pm    Post subject: Reply with quote

It didn't help in the end, but I noticed that r7c7 (67) and r8c6 (67) were locked together by r7c4 (67); that is r7c7 and r8c6 are either both 6 or are both 7.

There is a potential 23-7 XY pivoted in r1c8, but there is no single cell seen by both pincers with a 7 candidate. However, my two locked cells, r7c7 and r8c6, both had a 7 candidate and were both seen by one of my pincers. Therefore if I treat the locked cells as one, neither can be 7, so both are set to 6.

But, even so, I still needed two XYs after that to solve. Darn.


Last edited by rmireland on Sat May 30, 2015 11:57 pm; edited 2 times in total
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Marty R.



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

PostPosted: Sat May 30, 2015 10:42 pm    Post subject: Reply with quote

Code:

+----------+----------+------------+
| 9  6  37 | 8  1 27  | 4    23  5 |
| 37 1  4  | 67 5 267 | 238  238 9 |
| 5  2  8  | 9  3 4   | 1    6   7 |
+----------+----------+------------+
| 6  9  23 | 4  7 38  | 28   5   1 |
| 37 8  5  | 1  2 39  | 79   4   6 |
| 1  4  27 | 5  6 89  | 2789 278 3 |
+----------+----------+------------+
| 8  3  9  | 67 4 5   | 67   1   2 |
| 2  57 1  | 3  8 67  | 567  9   4 |
| 4  57 6  | 2  9 1   | 357  37  8 |
+----------+----------+------------+

Play this puzzle online at the Daily Sudoku site

I usually try to solve these using the standard VH moves, but I didn't see it, so I used coloring (if that's the right term) on 7.
(7=6)r7c7-(6=7)r7c4-(6=7)r8c6-r12c6=r2c4-r2c1=r5c1=>r5c7<>7
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rmireland



Joined: 21 Sep 2013
Posts: 33
Location: New Orleans

PostPosted: Sun May 31, 2015 12:12 am    Post subject: Reply with quote

Hi Marty,
We've had a real drought of Eureka lately, so I'm glad to see a few sprinkles. However, I don't follow your logic. If I understand it, you are essentially saying "If r7c7 were a 7 then ... r5c7 <> 7" by following your path.
But if r7c7 were 7, then r5c7 <> 7 directly, and the path doesn't seem to add anything. If you ended in a contradiction, then you would have something important.
Don't you need a second path that traces "If r7c7 were a 6 then ... r5c7<>7" or a path that says "If r7c7 were 7 then ... r5c7=7" as a contradiction?
Just wondering,
Rick
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Marty R.



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

PostPosted: Sun May 31, 2015 12:38 am    Post subject: Reply with quote

Rick,

The first term (7=6)r7c7 says if that cell is NOT 7, then r5c1 IS a 7. R5c7 is toast because it sees both the start and end of the chain. Remember that in a strong inference, as indicated by an = sign, the number to the left of the = sign is always false and the one to the right is true.

Marty
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

PostPosted: Sun May 31, 2015 2:03 pm    Post subject: Reply with quote

Marty R. wrote:
Code:

+----------+----------+------------+
| 9  6  37 | 8  1 27  | 4    23  5 |
| 37 1  4  | 67 5 267 | 238  238 9 |
| 5  2  8  | 9  3 4   | 1    6   7 |
+----------+----------+------------+
| 6  9  23 | 4  7 38  | 28   5   1 |
| 37 8  5  | 1  2 39  | 79   4   6 |
| 1  4  27 | 5  6 89  | 2789 278 3 |
+----------+----------+------------+
| 8  3  9  | 67 4 5   | 67   1   2 |
| 2  57 1  | 3  8 67  | 567  9   4 |
| 4  57 6  | 2  9 1   | 357  37  8 |
+----------+----------+------------+

Play this puzzle online at the Daily Sudoku site

I usually try to solve these using the standard VH moves, but I didn't see it, so I used coloring (if that's the right term) on 7.
(7=6)r7c7-(6=7)r7c4-(6=7)r8c6-r12c6=r2c4-r2c1=r5c1=>r5c7<>7


Marty, I suggest you review your third term, -(6=7)r8c6. It should be -(7=6)r8c6 which does not lead to you deletion.
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Marty R.



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

PostPosted: Sun May 31, 2015 4:01 pm    Post subject: Reply with quote

Thanks Ted, consider it reviewed. Laughing Embarassed
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