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July 31 VH

 
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RobertRattley



Joined: 24 Jun 2007
Posts: 58
Location: Australia

PostPosted: Wed Jul 30, 2014 8:39 pm    Post subject: July 31 VH Reply with quote

Early hint from my time zone advantage:

xy wing with pivot in row 8 column 1 (after finding a pair in row 2)
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Clement



Joined: 24 Apr 2006
Posts: 686
Location: Dar es Salaam Tanzania

PostPosted: Wed Jul 30, 2014 10:47 pm    Post subject: Jul 31 VH Reply with quote

Code:

+----------------+-------------+------------+
| 37-2  *23   8    | 1   237 5   | 6   9  4   |
| 357-2 1    6    | 348 9   478 | 378 25 38  |
| 9    4    57   | 38  237 6   | 378 25 1   |
+----------------+-------------+------------+
| 4    59   59   | 7   8   2   | 1   3  6   |
| 1    7    3    | 49  6   49  | 2   8  5   |
| 6    8    2    | 5   1   3   | 9   4  7   |
+----------------+-------------+------------+
| 8    #35   1457 | 2   357 17  | 34  6  9   |
| *23   6    19   | 389 4   189 | 5   7  238 |
| 2357 2359 4579 | 6   357 789 | 348 1  238 |
+----------------+-------------+------------+
XY-Wing 35-2 pivoted in r7c2; r12c1<>2; stte.
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rmireland



Joined: 21 Sep 2013
Posts: 15
Location: New Orleans

PostPosted: Thu Jul 31, 2014 3:51 pm    Post subject: Reply with quote

Clement, what is the path to eliminate -2r1c1 when r7c2 is 5? In my solution r1c1 = 2.
Thanks, Rick (temp in Mumbai)
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Dart45



Joined: 16 Apr 2008
Posts: 17
Location: Canada

PostPosted: Thu Jul 31, 2014 4:53 pm    Post subject: Reply with quote

OK, to be sure, I have solved today's puzzle twice, without having to use any of the VERY HARD techniques. Just a straightforward HARD puzzle the way I see it. Anyone else? Dart
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Thu Jul 31, 2014 4:59 pm    Post subject: Reply with quote

There seems to be something strange about the XY-Wing shown. Instead of consisting of XY-XZ-YZ, it consists of XY-XZ-XZ.
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rmireland



Joined: 21 Sep 2013
Posts: 15
Location: New Orleans

PostPosted: Thu Jul 31, 2014 5:58 pm    Post subject: Reply with quote

After further review, I believe Clement just oversold his wing. His basics aren't quite complete, but the pivot does lead to -2r2c1 with ste. However, it does not lead to -2r1c1 as claimed, and it is a stretch to call that thing an XY wing. I am sure Dan has a name for it, though.
To Dart: please post your after-basics grid and we will take a look (lol). I needed the same XY as Robert.
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mqllove



Joined: 07 Jan 2014
Posts: 13

PostPosted: Thu Jul 31, 2014 6:08 pm    Post subject: Re: Jul 31 VH Reply with quote

Clement wrote:
Code:

+----------------+-------------+------------+
| 37-2  *23   8    | 1   237 5   | 6   9  4   |
| 357-2 1    6    | 348 9   478 | 378 25 38  |
| 9    4    57   | 38  237 6   | 378 25 1   |
+----------------+-------------+------------+
| 4    59   59   | 7   8   2   | 1   3  6   |
| 1    7    3    | 49  6   49  | 2   8  5   |
| 6    8    2    | 5   1   3   | 9   4  7   |
+----------------+-------------+------------+
| 8    #35   1457 | 2   357 17  | 34  6  9   |
| *23   6    19   | 389 4   189 | 5   7  238 |
| 2357 2359 4579 | 6   357 789 | 348 1  238 |
+----------------+-------------+------------+
XY-Wing 35-2 pivoted in r7c2; r12c1<>2; stte.


Chiming in timidly, there are lots of people here smarter than I am. Before removing the 2s in box 1, please notice the naked quad in row 2 which removes 3 & 7 from r2c1, which in turn exposes the XY-wing. To be honest, I didn't find it, I cheated by having another program solve it when I was seriously stumped and of course could have kicked myself when the other program highlighted the quad. Embarassed
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Dart45



Joined: 16 Apr 2008
Posts: 17
Location: Canada

PostPosted: Thu Jul 31, 2014 7:08 pm    Post subject: Reply with quote

Rmireland - LOL - The grid after basics is the solved puzzle. As I said, I did not need any of the advanced techniques to solve it. Purely basics, which is why I double checked it.
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kuskey



Joined: 10 Dec 2008
Posts: 127
Location: Pembroke, NH

PostPosted: Thu Jul 31, 2014 11:39 pm    Post subject: 31 June VH Reply with quote

In my opinion, this puzzle is your run-of-the-mill
VH, although somewhat challenging. RobertRattley got it correct right out of the box- a 235 xy wing but didn't mention that there are two sets of cells, which is fairly common. What is somewhat rare, both sets remove 5 in r9c1. Mqllove got it after assistance. Clement, I can't find a 235 xy that has a pivot in r7c2 (perhaps a typo). And Dart45, with all due respect give me some help finding this puzzle to be HARD only.
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dongrave



Joined: 06 Mar 2014
Posts: 59

PostPosted: Fri Aug 01, 2014 12:59 am    Post subject: Reply with quote

I think that RobertRattley was almost right but the XY pivot looks like it's actually at r1c2 (r2c1=25, r1c2=23, r7c2=35) which eliminates the 5 from r9c1 which forces r2c1 to be 5. But the hardest part for me was first finding that darn hidden 2-5 pair in r2. Hey Dart, try it one more time and write the steps down as you solve it (e.g. 1. r1c4=1, 2. r5c5=56, etc.) so we can see it. I think you'll find that it requires a VH move. Don.
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dongrave



Joined: 06 Mar 2014
Posts: 59

PostPosted: Fri Aug 01, 2014 1:19 am    Post subject: Reply with quote

Hey! I just noticed that RobertRattley's XY wing DOES seem to solve it! I didn't see that one! His XY is r2c1=25, r8c1=23, r7c2=35 which also solves it!
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Fri Aug 01, 2014 4:12 am    Post subject: Reply with quote

Like Clement, i also missed the quad in r2. Here's my grid after accounting for that quad:

Code:

+----------------+-------------+------------+
| 237  23   8    | 1   27  5   | 6   9  4   |
| 25   1    6    | 348 9   478 | 378 25 38  |
| 9    4    57   | 38  237 6   | 378 25 1   |
+----------------+-------------+------------+
| 4    59   59   | 7   8   2   | 1   3  6   |
| 1    7    3    | 49  6   49  | 2   8  5   |
| 6    8    2    | 5   1   3   | 9   4  7   |
+----------------+-------------+------------+
| 8    35   1457 | 2   357 17  | 34  6  9   |
| 23   6    19   | 389 4   189 | 5   7  238 |
| 2357 2359 4579 | 6   357 789 | 348 1  238 |
+----------------+-------------+------------+

Play this puzzle online at the Daily Sudoku site

Dart, where did you go from this position?
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dongrave



Joined: 06 Mar 2014
Posts: 59

PostPosted: Fri Aug 01, 2014 12:09 pm    Post subject: Reply with quote

The hidden 2-5 pair in row 2 (cols 1 and 8) was a lot easier for me to find than the hidden quad and it gets you to the same place.
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Fri Aug 01, 2014 3:03 pm    Post subject: Reply with quote

dongrave wrote:
The hidden 2-5 pair in row 2 (cols 1 and 8) was a lot easier for me to find than the hidden quad and it gets you to the same place.


Even though I missed this quad, triples, quads, etc., are easier for me to find. But it's six of one, half-dozen of the other; hidden pairs, triples, etc., are always complemented by a subset. Whatever works.
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dongrave



Joined: 06 Mar 2014
Posts: 59

PostPosted: Sat Aug 02, 2014 1:12 am    Post subject: Reply with quote

Hi Marty, That's interesting! I don't think I'll ever find it easier to see a hidden quad than a hidden pair! Oh well, like you said, whatever works. Hey! I hope you're not holding your breath to hear back from Dart. He probably realizes his error by now (lol). I looked at this problem long enough to go out on a limb and say that it cannot be solved using just the basics. And I'm sure that you know that too. Oh well, it happens. You might remember not long ago when I was SURE that I had solved a VH twice using just the basics so I asked you about it. You advised me to get the eraser out so I did - and sure enough, on my 3rd attempt... (time to click on embarrassed face).
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Sat Aug 02, 2014 1:45 am    Post subject: Reply with quote

Earlier in my time on the forum I was burned a few times by declaring a puzzle solvable with basics only. That'll get you to think a little differently as to how to approach that situation. Laughing
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Clement



Joined: 24 Apr 2006
Posts: 686
Location: Dar es Salaam Tanzania

PostPosted: Sun Aug 03, 2014 11:32 pm    Post subject: Jul 31 VH Reply with quote

Sorry Members. A real blunder Embarassed
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