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5/20/07 Nightmare...7's grid

 
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Sudtyro
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Joined: 16 Jan 2007
Posts: 49

PostPosted: Wed Jun 20, 2007 6:03 pm    Post subject: 5/20/07 Nightmare...7's grid Reply with quote

The following 7's grid was derived from the full puzzle after running through the basics, and after two short Turbot chains and one XY-Wing.

Code:
. 7 . | . . 7 | . . .
. . . | . . . | . . .
. 7 . | 7 . . | . . .
------+-------+------
. . . | 7 . . | . . 7
. . . | 7 . 7 | 7 . .
. . . | . . . | . . .
------+-------+------
7 . . | . . . | . . 7
7 . . | . . . | 7 . 7
. . . | . . . | . . .


I'm working with this grid as part of a new ALS search strategy to be posted soon. But, now I'm totally Para-noid! Smile
Please tell me....is there a fish in here?
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Ruud
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Joined: 30 Dec 2005
Posts: 601

PostPosted: Wed Jun 20, 2007 6:38 pm    Post subject: Reply with quote

Sudtyro wrote:
is there a fish in here?

No
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“If the human brain were so simple that we could understand it, we would be so simple that we couldn't.” - Emerson M Pugh
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Myth Jellies
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Joined: 04 Apr 2006
Posts: 42

PostPosted: Thu Jun 21, 2007 7:30 am    Post subject: Reply with quote

There is a trick.

For there to be a stand-alone fish, you have to be able to have candidates seeing each other in a loop through the unsolved boxes. With this setup, the only cyclic path through any of the unsolved boxes would be b1-b2-b5-b6-b9-b7-b1.... Since the candidates in b1 and b7 cannot directly see each other, there is no cyclic box path so there won't be a useful stand-alone fish or coloring reduction (outside of possibly a line-box or box-box locked candidates deduction).
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Sudtyro
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Joined: 16 Jan 2007
Posts: 49

PostPosted: Thu Jun 21, 2007 4:21 pm    Post subject: Reply with quote

Myth Jellies wrote:
There is a trick.


Thanks, MJ...that's really helpful!
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Sudtyro
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Joined: 16 Jan 2007
Posts: 49

PostPosted: Tue Jul 03, 2007 4:57 pm    Post subject: Reply with quote

MJ,

One quick follow-up question on your "trick"...
Does “stand-alone” mean naked only, or can a successful cyclic path also indicate a possible hidden fish?
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Myth Jellies
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Joined: 04 Apr 2006
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PostPosted: Wed Jul 04, 2007 7:02 am    Post subject: Reply with quote

I am not sure what a hidden fish is. Unlike locked sets where a naked set is coupled with a hidden set, a fish group is always coupled with just another fish group.

By stand-alone, I meant a fish deduction that could not be represented more simply, like with a hidden single or locked candidates deduction.

To show what I mean, in your example, pretend that the 7 in r4c4 does not exist. Then you would have an r135/c246 swordfish acting to eliminate r5c7, but you would also have the simpler locked candidates in box 5 row 5 making the same deduction.
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Sudtyro
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Joined: 16 Jan 2007
Posts: 49

PostPosted: Wed Jul 04, 2007 10:45 am    Post subject: Reply with quote

Got it...thanks!
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