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Jan 13 VH

 
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Earl



Joined: 30 May 2007
Posts: 635
Location: Victoria, KS

PostPosted: Tue Jan 13, 2009 3:51 am    Post subject: Jan 13 VH Reply with quote

After a week's wait for a VH, an xy-wing (679) does it.

Earl
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cgordon



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

PostPosted: Tue Jan 13, 2009 12:22 pm    Post subject: Reply with quote

Same for me. Kinda disappointing. Crying or Very sad
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Wendy W



Joined: 04 Feb 2008
Posts: 144

PostPosted: Tue Jan 13, 2009 11:03 pm    Post subject: Reply with quote

It's even worse for me. The past 2 VH puzzles I've done with no advanced techniques whatsoever. One I'd put down to luck -- or a mistake. But two in a row?!
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daj95376



Joined: 23 Aug 2008
Posts: 3854

PostPosted: Tue Jan 13, 2009 11:41 pm    Post subject: Reply with quote

Maybe you won't find my Set H Puzzle 85 so trivial.
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Marty R.



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

PostPosted: Wed Jan 14, 2009 1:38 am    Post subject: Reply with quote

Wendy W wrote:
It's even worse for me. The past 2 VH puzzles I've done with no advanced techniques whatsoever. One I'd put down to luck -- or a mistake. But two in a row?!

Wendy, when that happens, do you ever try it a second time? I have and have been unable to duplicate my first solution at times.
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keith



Joined: 19 Sep 2005
Posts: 3344
Location: near Detroit, Michigan, USA

PostPosted: Wed Jan 14, 2009 5:22 pm    Post subject: Reply with quote

After basics:
Code:
+----------------+----------------+----------------+
| 2    5    39   | 4679 367  3467 | 8    37   1    |
| 79a 67-9 367-9 | 1    8    2    | 39b  4    5    |
| 4    1    8    | 79   5    37   |2-39  237  6    |
+----------------+----------------+----------------+
| 59   69   2    | 3    1    8    | 7    56   4    |
| 3    8    67   | 45   67   45   | 1    9    2    |
| 57d  4    1    | 267  267  9    | 35c 3-56  8    |
+----------------+----------------+----------------+
| 8    23   5    | 26   9    36   | 4    1    7    |
| 6    79   79   | 8    4    1    | 25   25   3    |
| 1    23   4    | 257  237  357  | 6    8    9    |
+----------------+----------------+----------------+
Take a look at a-b-c-d-a. The solutions are:
Code:
7  9

5  3

or
Code:
9  3

7  5
and you can make the eliminations shown.

Keith
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Marty R.



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

PostPosted: Wed Jan 14, 2009 6:07 pm    Post subject: Reply with quote

Keith, is that considered a standard XY-Chain or is there something else about it?
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keith



Joined: 19 Sep 2005
Posts: 3344
Location: near Detroit, Michigan, USA

PostPosted: Wed Jan 14, 2009 8:32 pm    Post subject: Reply with quote

Marty R. wrote:
Keith, is that considered a standard XY-Chain or is there something else about it?

Marty,

Sudoku Susser calls it a loop. (Edit: I also just saw a mention of a "bidirectional cycle" which is probably the same thing. Or, maybe it is a bicycle with a reverse gear.)

It is bidirectional. For example, choose <7> in a, the implications traverse the loop counter-clockwise. Choose <9>, the implications are clockwise.

You can see how I found it. I was looking for an extended XY-wing. We have 79 - 39 - 35 - 57. Regard any two adjacent cells as a pseudocell, for example 79 - (59) - 57 and you have an XY-wing.

The point is that the pincer cells a and d can see each other. You may recall that re'born pointed this out in an M-wing a couple of weeks ago.
http://dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=2143
If the pincer cells are peers (buddies) then you have a loop, and each pair of adjacent cells in the chain potentially makes eliminations.

I don't know if these are rare or not. They are not often mentioned, which may be because most solvers (human and otherwise) do not look for them.

Keith


Last edited by keith on Wed Jan 14, 2009 10:24 pm; edited 1 time in total
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Jan 14, 2009 9:14 pm    Post subject: Reply with quote

Keith,
I wouldn't say they are rare.
Myth Jellies calls them a Bi-location Loop in his players forum post on AIC's. this is a special case of a AIC loop because each cell contains only two candidates. the two candidates within the cell are connected strongly, and the cells are connected weakly.
since the loop connects the bi-value cells weakly, you can cut the loop at any of those weak links and still have a true xy-chain.
this will make the eliminations you pointed out.


yours is a square and therefore more easily recognized, some can get very elaborate especially if they involve more than 5 cells and two or more cells occur in the same box Smile

Code:
                  not2            not5

                  not2            not5

                  not2            not5

not4, not4, not4  (4=2)---not4----(5=4)  not4, not4, not4
                   |                |
                   |                |
                   |                |
                  not2            not5
                   |                |
                   |                |
                   |                |
not8, not8, not8  (2=8)---not8----(8=5)  not8, not8, not8

                  not2            not5

                  not2            not5
 
                  not2            not5


(4=2)-(2=8}-(8=5)-(5=4)

edit: corrected for errors


Last edited by storm_norm on Wed Jan 14, 2009 10:25 pm; edited 1 time in total
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keith



Joined: 19 Sep 2005
Posts: 3344
Location: near Detroit, Michigan, USA

PostPosted: Wed Jan 14, 2009 10:05 pm    Post subject: Reply with quote

Norm,
Quote:
some can get very elaborate especially if they involve more than 5 cells

You mean, like this:
Code:
+----------------+----------------+----------------+
| 2    5    39   | 4679 367  3467 | 8    37   1    |
| 79a  679  3679 | 1    8    2    | 39b  4    5    |
| 4    1    8    | 79   5    37   | 239  237  6    |
+----------------+----------------+----------------+
| 59h  69g  2    | 3    1    8    | 7    56f  4    |
| 3    8    67   | 45   67   45   | 1    9    2    |
| 57i  4    1    | 267  267  9    | 35c  356  8    |
+----------------+----------------+----------------+
| 8    23   5    | 26   9    36   | 4    1    7    |
| 6    79   79   | 8    4    1    | 25d  25e  3    |
| 1    23   4    | 257  237  357  | 6    8    9    |
+----------------+----------------+----------------+


Keith


Last edited by keith on Wed Jan 14, 2009 10:31 pm; edited 1 time in total
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sudocraz



Joined: 28 Apr 2008
Posts: 53

PostPosted: Thu Jan 15, 2009 2:13 am    Post subject: Reply with quote

At least my husband and I are getting a lot of practice with xy-wings. We are pretty good with them now. They even might be beginning to be a little boring. Laughing

Are the xyz wings pretty much the same as xy-wings, except one square , I assume the pivot square, has 3 numbers?
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DennyOR



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

PostPosted: Thu Jan 15, 2009 9:44 pm    Post subject: Reply with quote

A 79s w-wing in columns 1 and 2 did it for me.
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