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daj95376
Joined: 23 Aug 2008
Posts: 3854
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 Posted: Mon Apr 19, 2010 12:53 pm Post subject: Puzzle 10/04/19 (C) |
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| Code: | +-----------------------+
| . . . | . . 2 | 5 . 7 |
| . 6 . | . . . | 9 8 . |
| . . . | . 1 . | . . . |
|-------+-------+-------|
| . . . | 2 8 . | . 4 . |
| . . 6 | 4 9 . | 2 . 8 |
| 4 . . | . . 1 | . 9 5 |
|-------+-------+-------|
| 6 1 . | . 7 . | . 2 . |
| . 8 . | 1 . 4 | 7 . . |
| 5 . . | . 2 8 | . . . |
+-----------------------+
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Play this puzzle online at the Daily Sudoku site |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Mon Apr 19, 2010 5:02 pm Post subject: |
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This was very nice and involves a concatenation of ideas.
| Quote: | There is a nearly xy-wing of 134 (in blue) it has a fin 6 on r4c9.
But what about that 6 ? Well let's say the 6 in r4c9 is true - follow the chain of events in the strong links on 6 and we end up with a contradiction which sets two 6s on row 4 to true:
(13=6)r4c9-r8c9=r5c8-r6c5=(6)r4c6 which is a contradiction so r4c9<>6
Now the xy-wing is true then r46c7 <> 3 (in pink) and the puzzle is solved.
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Mon Apr 19, 2010 6:54 pm Post subject: |
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Interesting how the almost/nearly/Kraken XY-Wing caught your attention and you worked your way through it.
My poor solver broke you solution into two steps: turbot fish alternatives for r4c9<>6, and XY-Wing.
Personally, I find solutions like yours much more interesting -- an understandable base condition followed by an easy to follow extension!!! Thanks! |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Mon Apr 19, 2010 7:33 pm Post subject: |
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Funnily it is just like last time - sensate focus!
The subject on the card today is the finned XY wing which Ted introduced and has attracted much discussion.
For some reason I started looking for them and that started the ball rolling (I nearly said "chain of thought" but that would be cruel and unusual punishment!). |
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Luke451
Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California
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| Posted: Mon Apr 19, 2010 8:33 pm Post subject: |
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| Mogulmeister wrote: | This was very nice and involves a concatenation of ideas.
| Quote: | There is a nearly xy-wing of 134 (in blue) it has a fin 6 on r4c9.
But what about that 6 ? Well let's say the 6 in r4c9 is true - follow the chain of events in the strong links on 6 and we end up with a contradiction which sets two 6s on row 4 to true:
(13=6)r4c9-r8c9=r5c8-r6c5=(6)r4c6 which is a contradiction so r4c9<>6
Now the xy-wing is true then r46c7 <> 3 (in pink) and the puzzle is solved.
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| Quote: | |
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I'm confused, Mogul. Any elimination has to be he product of both the structure (the xy-wing) and the almost value (6)r4c9. The best I can get is this: | Code: | | xy-wing(134)r3c7,r24c9=(6)r4c9-(6=3)r6c7 =>r4c7<>3 |
Am I missing something again? |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Mon Apr 19, 2010 9:25 pm Post subject: |
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| Luke451 wrote: | I'm confused, ...
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It's a chain in the sense that you assume a false condition and then prove it true.
(14+3)xy-wing = (6)r4c9 - r8c9 = r8c5 - r6c5 = r4c6 - (6)r4c9 = (14+3)xy-wing
Using a turbot fish first on <6> would have broken it into two simpler steps.
FWIW: The eliminations may read better as RonK and Asellus might present it.
(3)r46c7 - (14+3)xy-wing = (6)r4c9 - r8c9 = r8c5 - r6c5 = r4c6 - (6)r4c9 = (14+3)xy-wing - (3)r46c7 |
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peterj
Joined: 26 Mar 2010
Posts: 974
Location: London, UK
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| Posted: Tue Apr 20, 2010 4:22 pm Post subject: |
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Hmm... my grid after basics still has a 6 in r3c6 and r9c8? I need a kite and then pointing to get rid of them?
Anyway I did lots of colouring on 6s and then the xy-wing.... |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Tue Apr 20, 2010 5:20 pm Post subject: |
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| peterj wrote: | Hmm... my grid after basics still has a 6 in r3c6 and r9c8? I need a kite and then pointing to get rid of them?
Anyway I did lots of colouring on 6s and then the xy-wing.... |
Yes, Mogulmeister failed to mention that he performed more than basics to arrive at his grid. In his defense, he never claimed that he had a single stepper solution.
Although a graphics display of a grid can be very informative to share one's point of view, failing to include a textual grid makes it difficult for others (like me) to examine the grid independent of the original viewpoint. |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Wed Apr 21, 2010 1:36 pm Post subject: Temp |
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Correct - I wasn't making any special stepper claims - more the way the end game presented itself which is much more interesting (to me).
[Edit] The grid you see above was arrived at after the first move which was an xy chain on 6s (pincers at r3c6 and r6c7) which is why the 6s are gone from r3c7 and the subsequent box/line which removes the 6 at r9c8.
Peter, It still has a 6 in r3c6. [/Edit]
Last edited by Mogulmeister on Wed Apr 21, 2010 2:11 pm; edited 6 times in total |
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tlanglet
Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
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| Posted: Wed Apr 21, 2010 1:44 pm Post subject: |
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Good Job Mogulmeister 
Glad I was able to induce someone else to consider "unusual" patterns.
Ted |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Wed Apr 21, 2010 1:56 pm Post subject: |
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| Great puzzle though. I think you should offer your services to Kate Mepham!! |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Wed Apr 21, 2010 4:41 pm Post subject: |
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Skyscraper (6)
XY-Wing (143)
W-Wing (13) |
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