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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Sun Sep 21, 2008 1:26 pm Post subject: Sept 21 VH |
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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
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| Posted: Sun Sep 21, 2008 1:33 pm Post subject: |
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Ditto.
Ted |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sun Sep 21, 2008 4:19 pm Post subject: |
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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
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| Posted: Sun Sep 21, 2008 5:21 pm Post subject: The boring old W Wing |
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| 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
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| Posted: Sun Sep 21, 2008 7:56 pm Post subject: |
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| 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: 1111
Location: Dar es Salaam Tanzania
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| Posted: Sun Sep 21, 2008 8:35 pm Post subject: Daily Sudoku: Sun 21-Sep-2008 VH |
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| 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
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| Posted: Sun Sep 21, 2008 9:38 pm Post subject: |
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| 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
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| Posted: Sun Sep 21, 2008 9:50 pm Post subject: |
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| 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
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| Posted: Sun Sep 21, 2008 10:08 pm Post subject: |
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| 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
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| Posted: Sun Sep 21, 2008 10:11 pm Post subject: |
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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
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| Posted: Mon Sep 22, 2008 3:33 am Post subject: |
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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
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| Posted: Sun Sep 28, 2008 11:49 pm Post subject: Sept 21 VH |
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Keith,
thanks for your XY wings finding guide, gives me new hope. Very helpful indeed !
Coruja  |
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