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Sept 21 VH

 
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Earl



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

PostPosted: Sun Sep 21, 2008 1:26 pm    Post subject: Sept 21 VH Reply with quote

An xy-wing eliminates 6's in box 6 and solves the puzzle.

Earl
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tlanglet



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

PostPosted: Sun Sep 21, 2008 1:33 pm    Post subject: Reply with quote

Ditto.

Ted
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keith



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

PostPosted: Sun Sep 21, 2008 4:19 pm    Post subject: Reply with quote

Yes, pretty easy. There are no pairs or line-box intersections needed.

Keith
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Sun Sep 21, 2008 5:21 pm    Post subject: The boring old W Wing Reply with quote

Having found a pretty useless XY wing to give the 3 in box 6 I found the W wing 46 to give the 9 in box 3 and solve the problem. Pity 'cos I find XY wings so hard to spot, and finding a useless one doesn't help the confidence!
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cgordon



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

PostPosted: Sun Sep 21, 2008 7:56 pm    Post subject: Reply with quote

Quote:
Pity 'cos I find XY wings so hard to spot

You an me both Bro. Looked in vain for ER's and UR's and other fancy stuff - then took forever to find the xy wing (actually I had to use two - based on the same triple).
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Clement



Joined: 24 Apr 2006
Posts: 1110
Location: Dar es Salaam Tanzania

PostPosted: Sun Sep 21, 2008 8:35 pm    Post subject: Daily Sudoku: Sun 21-Sep-2008 VH Reply with quote

XY-Wing 469 with Pivot in r1c8 eliminating 6's in r56c9 solves the puzzle.
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keith



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

PostPosted: Sun Sep 21, 2008 9:38 pm    Post subject: Reply with quote

cgordon wrote:
Quote:
Pity 'cos I find XY wings so hard to spot

You an me both Bro.

If you fill in only singles, and only pencil marks for 2-candidate cells, you get here:
Code:
+----------+----------+----------+
| 1  .  5  | 6  8  47 | 3  49 2  |
| 2  .  .  | 3  5  47 | 46 1  69 |
| 3  46 46 | 9  1  2  | 5  7  8  |
+----------+----------+----------+
| 46 3  .  | 5  2  .  | .  .  7  |
| 5  .  9  | 8  .  1  | 2  46 36 |
| 8  2  .  | 47 .  .  | .  5  .  |
+----------+----------+----------+
| 7  5  2  | 1  6  8  | 9  3  4  |
| .  1  .  | ,  .  3  | 68 .  5  |
| .  .  3  | 24 49 5  | 7  .  1  |
+----------+----------+----------+

The XY-wing 46-49-69 is, I think, pretty easy to spot. It solves R5C9 as <3>, and eliminates other candidates <6> in B6.

There is a systematic way to search for XY-wings. A guide, as I recall, was written by either ravel or Myth Jellies.

Best wishes,

Keith
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Sep 21, 2008 9:50 pm    Post subject: Reply with quote

Not too long ago nataraj wrote up such description of a systematic way to hunt for XY-Wings (and X-Wings as well) on this discussion board.
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cgordon



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

PostPosted: Sun Sep 21, 2008 10:08 pm    Post subject: Reply with quote

Thanks for xy-wing searching help, but for me - ER's and UR's can be found by looking for rectangular associations. Whereas I am not convinced there is any way to look for wings that is not painful.
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keith



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

PostPosted: Sun Sep 21, 2008 10:11 pm    Post subject: Reply with quote

Asellus,

Thank you for remembering! I was thinking of a different thread, but the one by Nataraj is great. Remember, turn up the sound!

Keith
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keith



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

PostPosted: Mon Sep 22, 2008 3:33 am    Post subject: Reply with quote

Here's how I do it. It took a while to figure out, and a longer while to use it routinely.

The puzzle of this thread:

Code:
+----------+----------+----------+
| 1  .  5  | 6  8  47 | 3  49 2  |
| 2  .  .  | 3  5  47 | 46 1  69 |
| 3  46 46 | 9  1  2  | 5  7  8  |
+----------+----------+----------+
| 46 3  .  | 5  2  .  | .  .  7  |
| 5  .  9  | 8  .  1  | 2  46 36 |
| 8  2  .  | 47 .  .  | .  5  .  |
+----------+----------+----------+
| 7  5  2  | 1  6  8  | 9  3  4  |
| .  1  .  | ,  .  3  | 68 .  5  |
| .  .  3  | 24 49 5  | 7  .  1  |
+----------+----------+----------+

Put in pencil marks only for cells with two candidates, which reduces the clutter. Scan from left to right, top to bottom.

1. The first two-candidate cell to consider is <47> in R1C6. Does it see any other two-candidate cells that contain <4> or <7>?

1a. Yes, <49> in R1. So, do either of these cells see a two-candidate cell <79>? No, sorry Charlie, no XY-wing here.

1b. Yes, <47> in in R2. Sorry, Charlie, pairs do not make wings.

2. The next two-candidate cell to consider is <49> in R1C8. Does it see any other two-candidate cells that contain <4> or <9>?

You do not have to look back at the <47> in R1. It has already been considered.

2a. Yes, <46> in R2. So, do either of these cells see a two-candidate cell <69>?.

2a1. Yes, <69> in in B3. Sorry, Charlie, triples do not make wings.

2b. Yes, <69> in R2. So, do either of these cells see a two-candidate cell <46>?.

2b1. Yes! <46> in in R5C8. You have an XY-wing!

This takes out a few candidates <6>, and solves the puzzle.

Keith
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CORUJA



Joined: 16 Jun 2007
Posts: 15
Location: BRUMADINHO - MG; BRAZIL

PostPosted: Sun Sep 28, 2008 11:49 pm    Post subject: Sept 21 VH Reply with quote

Keith,
thanks for your XY wings finding guide, gives me new hope. Very helpful indeed !
Coruja Very Happy
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