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Oct 24 VH

 
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Earl



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

PostPosted: Fri Oct 24, 2008 2:01 am    Post subject: Oct 24 VH Reply with quote

6-7-8 xy-wing is sufficient. Apparent coloring (7) is not necessary.

Earl
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Fri Oct 24, 2008 2:44 am    Post subject: Re: Oct 24 VH Reply with quote

Earl wrote:
6-7-8 xy-wing is sufficient. Apparent coloring (7) is not necessary.

Earl


Anybody solve this without advanced techniques/wings?

Code:

+--------------+-----------+----------+
| 9   468 467  | 3   1  67 | 68 2  5  |
| 67  5   3    | 8   9  2  | 46 1  47 |
| 1   68  2    | 4   5  67 | 3  78 9  |
+--------------+-----------+----------+
| 3   7   9    | 6   8  5  | 2  4  1  |
| 4   2   8    | 1   7  3  | 9  5  6  |
| 56  1   56   | 9   2  4  | 7  3  8  |
+--------------+-----------+----------+
| 28  46  1    | 27  46 9  | 5  78 3  |
| 28  9   457  | 257 3  1  | 48 6  47 |
| 567 3   4567 | 57  46 8  | 1  9  2  |
+--------------+-----------+----------+

Play this puzzle online at the Daily Sudoku site
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tlanglet



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

PostPosted: Fri Oct 24, 2008 4:07 am    Post subject: Reply with quote

Another one-stepper is a w-wing <67> located at r1c6 & r2c1 with strong link <6> in col7. Deletion of <7> from r1c3 finishes off the puzzle.

Ted
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daj95376



Joined: 23 Aug 2008
Posts: 3854

PostPosted: Fri Oct 24, 2008 4:40 am    Post subject: Re: Oct 24 VH Reply with quote

crunched wrote:
Anybody solve this without advanced techniques/wings?

Code:
+--------------+-----------+----------+
| 9   468 467  | 3   1  67 | 68 2  5  |
| 67  5   3    | 8   9  2  | 46 1  47 |
| 1   68  2    | 4   5  67 | 3  78 9  |
+--------------+-----------+----------+
| 3   7   9    | 6   8  5  | 2  4  1  |
| 4   2   8    | 1   7  3  | 9  5  6  |
| 56  1   56   | 9   2  4  | 7  3  8  |
+--------------+-----------+----------+
| 28  46  1    | 27  46 9  | 5  78 3  |
| 28  9   457  | 257 3  1  | 48 6  47 |
| 567 3   4567 | 57  46 8  | 1  9  2  |
+--------------+-----------+----------+

From your PM:

Locked Candidate 1 => [r8c3]<>4
Skyscraper => [r8c3]<>7
Singles
BUG+1 => [r1c2]=6
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Fri Oct 24, 2008 1:54 pm    Post subject: Reply with quote

tlanglet wrote:
Another one-stepper is a w-wing <67> located at r1c6 & r2c1 with strong link <6> in col7. Deletion of <7> from r1c3 finishes off the puzzle.

Ted


My solver tool box uses the x, xy, xyz wings. That is essentially it.
I am trying to expand that. Why wouldn't the w-wing, pointed out here, eliminate both <6> & <7> in r1c3? If not both, why does it eliminate <7> rather than <6> ?
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Marty R.



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

PostPosted: Fri Oct 24, 2008 3:50 pm    Post subject: Reply with quote

Quote:
Why wouldn't the w-wing, pointed out here, eliminate both <6> & <7> in r1c3? If not both, why does it eliminate <7> rather than <6> ?


Have you read the W-Wing explanation here?

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=2143

Someone could probably give a better answer than I can, but with the strong link on 6 in column 7, that forces one or the other of the 67 pairs to be = 7, thus the 7s act as pincers.
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Clement



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

PostPosted: Fri Oct 24, 2008 5:07 pm    Post subject: Daily Sudoku: Fri 24-Oct-2008 VH Reply with quote

XY-Wing Pivot {6,8}r3c2 with Pincers in r2c1{6,7} and r3c8{7,8} eliminating 7 in r2c9 solves the puzzle.
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daj95376



Joined: 23 Aug 2008
Posts: 3854

PostPosted: Fri Oct 24, 2008 6:00 pm    Post subject: Reply with quote

Marty R. wrote:
Quote:
Why wouldn't the w-wing, pointed out here, eliminate both <6> & <7> in r1c3?
If not both, why does it eliminate <7> rather than <6> ?

... with the strong link on 6 in column 7, that forces one or the other of the 67 pairs to be = 7, thus the 7s act as pincers.

At the risk of repeating Marty's reply, there's an alternate way of viewing this 4-cell W-Wing. Work from the inside out!

Consider the strong link on 6 in [c7]. Either [r1c7]=6 or else [r2c7]=6.

Code:
 [r1c7]=6 => [r1c6]=7 => [r1c3]<>7
 [r2c7]=6 => [r2c1]=7 => [r1c3]<>7

 +--------------------------------------------------------------+
 |  9     468   46-7  |  3     1    #67    | *68    2     5     |
 | #67    5     3     |  8     9     2     | *46    1     47    |
 |  1     68    2     |  4     5     67    |  3     78    9     |
 |--------------------+--------------------+--------------------|
 |  3     7     9     |  6     8     5     |  2     4     1     |
 |  4     2     8     |  1     7     3     |  9     5     6     |
 |  56    1     56    |  9     2     4     |  7     3     8     |
 |--------------------+--------------------+--------------------|
 |  28    46    1     |  27    46    9     |  5     78    3     |
 |  28    9     457   |  257   3     1     |  48    6     47    |
 |  567   3     4567  |  57    46    8     |  1     9     2     |
 +--------------------------------------------------------------+

Although setting [r1c7]=6 will also produce the eliminations [r1c23]<>6, setting [r2c7]=6 does not produce either of these eliminations.

Now, to confuse you even further, there's also a strong link on 6 in [r3].

Wanna bet there's another 4-cell W-Wing for the same elimination?
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cgordon



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

PostPosted: Fri Oct 24, 2008 10:21 pm    Post subject: Reply with quote

There's an ER on 7 that gets rid of the 7 in R8C3.
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sat Oct 25, 2008 4:09 am    Post subject: Reply with quote

Marty R. wrote:
Quote:
Why wouldn't the w-wing, pointed out here, eliminate both <6> & <7> in r1c3? If not both, why does it eliminate <7> rather than <6> ?


Have you read the W-Wing explanation here?

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=2143


Someone could probably give a better answer than I can, but with the strong link on 6 in column 7, that forces one or the other of the 67 pairs to be = 7, thus the 7s act as pincers.


This strong link on 6 is considered a strong link because there are only 2 sixes in that column?


Yes, I have read the tutorial, and I need to keep referring back to it. This stuff does not immediately sink in. At some point I will get the "aha" moment and it will become easy to apply---I think!
It is a nice tutorial, thanks.
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sat Oct 25, 2008 4:11 am    Post subject: Reply with quote

This was good. I like the way you explained the logic involved in this.
Thanks.

daj95376 wrote:
Marty R. wrote:
Quote:
Why wouldn't the w-wing, pointed out here, eliminate both <6> & <7> in r1c3?
If not both, why does it eliminate <7> rather than <6> ?

... with the strong link on 6 in column 7, that forces one or the other of the 67 pairs to be = 7, thus the 7s act as pincers.

At the risk of repeating Marty's reply, there's an alternate way of viewing this 4-cell W-Wing. Work from the inside out!

Consider the strong link on 6 in [c7]. Either [r1c7]=6 or else [r2c7]=6.

Code:
 [r1c7]=6 => [r1c6]=7 => [r1c3]<7> [r2c1]=7 => [r1c3]<>7

 +--------------------------------------------------------------+
 |  9     468   46-7  |  3     1    #67    | *68    2     5     |
 | #67    5     3     |  8     9     2     | *46    1     47    |
 |  1     68    2     |  4     5     67    |  3     78    9     |
 |--------------------+--------------------+--------------------|
 |  3     7     9     |  6     8     5     |  2     4     1     |
 |  4     2     8     |  1     7     3     |  9     5     6     |
 |  56    1     56    |  9     2     4     |  7     3     8     |
 |--------------------+--------------------+--------------------|
 |  28    46    1     |  27    46    9     |  5     78    3     |
 |  28    9     457   |  257   3     1     |  48    6     47    |
 |  567   3     4567  |  57    46    8     |  1     9     2     |
 +--------------------------------------------------------------+

Although setting [r1c7]=6 will also produce the eliminations [r1c23]<>6, setting [r2c7]=6 does not produce either of these eliminations.

Now, to confuse you even further, there's also a strong link on 6 in [r3].

Wanna bet there's another 4-cell W-Wing for the same elimination?
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DennyOR



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

PostPosted: Sat Oct 25, 2008 7:58 pm    Post subject: Reply with quote

And the 68-87-74-46 chain also solves the puzzle.
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keith



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

PostPosted: Sat Oct 25, 2008 9:05 pm    Post subject: Reply with quote

crunched wrote:
This strong link on 6 is considered a strong link because there are only 2 sixes in that column?

Yes, I have read the tutorial, and I need to keep referring back to it. This stuff does not immediately sink in. At some point I will get the "aha" moment and it will become easy to apply---I think!
It is a nice tutorial, thanks.


This will get you to "Aha" much quicker:

http://www.sudoku.com/boards/viewtopic.php?t=3326

Best wishes,

Keith
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crunched



Joined: 05 Feb 2008
Posts: 168

PostPosted: Sun Oct 26, 2008 11:34 pm    Post subject: Reply with quote

Wow, that was a good tutorial on strong lengths and buddies. I think I will be able to put this to use, especially with skyscrapers---and 2-string kites too. Smile. Thanks for the heads-up on that!

keith wrote:
crunched wrote:
This strong link on 6 is considered a strong link because there are only 2 sixes in that column?

Yes, I have read the tutorial, and I need to keep referring back to it. This stuff does not immediately sink in. At some point I will get the "aha" moment and it will become easy to apply---I think!
It is a nice tutorial, thanks.


This will get you to "Aha" much quicker:

http://www.sudoku.com/boards/viewtopic.php?t=3326

Best wishes,

Keith
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