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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Sat May 09, 2009 12:20 pm Post subject: May 9 DB |
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The May 9 DB is cute. Two critical steps, both within in a four cell box, using only three numbers!
Solution: w-wing (48) followed by an xy-wing (348).
Earl
| Code: |
+-------+-------+-------+
| . 9 7 | . . . | . . 6 |
| 2 . . | . . 3 | 1 . . |
| . 6 . | . . . | 7 5 . |
+-------+-------+-------+
| . 1 . | . 4 7 | 6 . . |
| . . . | 9 . 6 | . . . |
| . . 6 | 2 5 . | . 4 . |
+-------+-------+-------+
| . 4 5 | . . . | . 3 . |
| . . 9 | 1 . . | . . 8 |
| 8 . . | . . . | 5 7 . |
+-------+-------+-------+
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Play this puzzle online at the Daily Sudoku site
Last edited by Earl on Sat May 09, 2009 4:55 pm; edited 1 time in total |
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Sat May 09, 2009 2:28 pm Post subject: |
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I don't understand the w-wing. Could someone explain it to me? Thanks.  |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Sat May 09, 2009 3:20 pm Post subject: |
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in this position
| Code: |
+--------------------------+--------------------------+--------------------------+
| 134 9 7 | 5 128 248 | 238 28 6 |
| 2 5 48* | 67 67 3 | 1 89 49# |
| 134 6 34-8 | 48* 1289 2489 | 7 5 234# |
+--------------------------+--------------------------+--------------------------+
| 359 1 23 | 38 4 7 | 6 289 2359 |
| 3457 378 234 | 9 38 6 | 238 1 2357 |
| 379 378 6 | 2 5 1 | 389 4 379 |
+--------------------------+--------------------------+--------------------------+
| 6 4 5 | 78 2789 289 | 29 3 1 |
| 37 237 9 | 1 23 5 | 4 6 8 |
| 8 23 1 | 346 2369 249 | 5 7 29 |
+--------------------------+--------------------------+--------------------------+
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The two ("pincer") cells r2c3 and r3c4 both have the same two candidates {4,8} AND each cells "sees" one end of a strong link (either (4)r2c9=r3c9 or (4)r1c1=r1c6) in one of the two candidates.
The other candidate must be present in at least one of the two pincer cells and therefore ...
Every cell that sees both pincers cannot contain the other candidate ("8").
Why?
Look at r2c3 (one of the pincers)
If it is 8, the assertion (every cell that sees r2c3 cannot be 8 ) is true
If it is not 8 (but 4), then r2c9 cannot be 4.
The strong link in col 9 then says r3c9 must be 4
But then .... r3c4 must be 8
Hope this helps |
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Sat May 09, 2009 5:17 pm Post subject: |
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Thanks nataraj for a detailed explanation. I read it a couple of times to understand it. Its helpful to understand a new technique when its on a puzzle I'm trying to solve. I will try to look for w-wings in the future.
How nice to get help all the way from Austria!
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Sat May 09, 2009 7:21 pm Post subject: |
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yw Louise,
indeed it is nice to meet people from across the globe here 
Looking for w-wings is easy: the two cells with the same two candidates are usually very obvious. All that remains to do is to look for the connecting strong link.
take care,
nataraj |
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