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pendrith
Joined: 07 Jul 2006 Posts: 3

Posted: Fri Jul 07, 2006 4:59 pm Post subject: July 6 puzzle 


I'm stuck on the July 6 puzzle. Can anyone explain the logic required to continue??
942567
173562948
8564312
29673
7825
63248
32879
87312
27836 

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David Bryant
Joined: 29 Jul 2005 Posts: 559 Location: Denver, Colorado

Posted: Fri Jul 07, 2006 6:11 pm Post subject: Row on block interaction 


To proceed you need to analyze where a "1" can fall in row 4.
 There cannot be a "1" at r4c1 because of the "1" at r2c1.
 Therefore the "1" in row 4 must fall in the middle center 3x3 box. This means that you can eliminate the possibility of a "1" in the rest of that box  at r5c46, and at r6c4&6, in other words.
 Now you can find a naked pair {7, 9} in column 4  at r3c4 & r6c4. So you can set r8c4 = 6, and the rest should be relatively straightforward. dcb 

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pendrith
Joined: 07 Jul 2006 Posts: 3

Posted: Mon Jul 10, 2006 2:41 pm Post subject: 


Hi David
Thanks for responding.
I'm still confused however.
No doubt finding where the "1" falls in row 4 would help solve the puzzle.
I understand how there cannot be a "1" at r4c1
However I don't see how you can eliminate a "1" at r4c4 or r4c6
What am I missing?? 

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Marty R.
Joined: 12 Feb 2006 Posts: 5225 Location: Rochester, NY, USA

Posted: Mon Jul 10, 2006 3:58 pm Post subject: 


Quote:  However I don't see how you can eliminate a "1" at r4c4 or r4c6 
I haven't yet done this puzzle and I'm not looking at any grid, but I'm not seeing where David said the "1" can be eliminated from those two cells. 

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ravel
Joined: 21 Apr 2006 Posts: 536

Posted: Mon Jul 10, 2006 4:14 pm Post subject: 


942xxx567
173562948
856x4x312

x29xxx673
78xxxx25x
63xx2x48x

3xx28x79x
xx8x7312x
2x7xxx836
To repeat in other words, what David said:
In row 4 the 1 must be in column 4,5 or 6. So box 5 must have the 1 in this row and it cannot be elsewhere in that box (this is called box/box interaction, Locked Candidates 2 or Claiming). Therefore only 79 remain for r6c4, the same we have in r3c4.
Same thing for the 4: In row 9 the 4 must be in column 4 or 6. Therefore it cannot be in r7c6 or r8c4.
Looking at the remaining candidates in r8c4 now, it cannot be 4 and it cannot be 9 from the 79pair in r36c4. Then only 6 is left. 

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pendrith
Joined: 07 Jul 2006 Posts: 3

Posted: Mon Jul 10, 2006 6:31 pm Post subject: 


Got it!
Thanks guys 

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TKiel
Joined: 22 Feb 2006 Posts: 292 Location: Kalamazoo, MI

Posted: Sat Aug 19, 2006 11:23 pm Post subject: 


ravel wrote:  In row 4 the 1 must be in column 4,5 or 6. So box 5 must have the 1 in this row and it cannot be elsewhere in that box (this is called box/box interaction...) 
I understand how this works, I just don't understand why it is called a box/box interaction. I quess I don't understand how a box could relate to another box except through a row or column and therefore why it wouldn't be a box/row interaction. 

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ravel
Joined: 21 Apr 2006 Posts: 536

Posted: Sun Aug 20, 2006 11:48 am Post subject: 


I agree, that its not the best name (as for some other techniques). I suppose, it comes from the fact, that with a "box/line interaction" (locked candidates 1) you can eliminate candidates in the line (row/column), whereas with "box/box interaction" you can eliminate them in the box. 

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TKiel
Joined: 22 Feb 2006 Posts: 292 Location: Kalamazoo, MI

Posted: Sun Aug 20, 2006 12:33 pm Post subject: 


Ravel,
Thanks. Your explanation was good enough to make the name seem logical. 

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keith
Joined: 19 Sep 2005 Posts: 3186 Location: near Detroit, Michigan, USA


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ravel
Joined: 21 Apr 2006 Posts: 536

Posted: Sun Aug 20, 2006 3:32 pm Post subject: Re: block  block interactions 


Ah, you found the link ! And yes, i think, it is unusual to spot box/box in the desribed way. This made it hard to understand the name. 

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TKiel
Joined: 22 Feb 2006 Posts: 292 Location: Kalamazoo, MI

Posted: Sun Aug 20, 2006 9:00 pm Post subject: 


The explanation on the Sadman site seems totally backward to me, although if one did manage to look at it that way, the name would make more sense.
If we can have umpteen UR's labeled Type 1, Type 2, etc... it seems we should be able to keep track of box/line Type 1 (locked candidates 1) and box/line Type 2 (locked candidates 2). Or maybe just box/line and line/box would work. Nah, too many people would think that was a misprint. Maybe it's time to organize a Sudoku board of governours to standardize/logisize terminology. 

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keith
Joined: 19 Sep 2005 Posts: 3186 Location: near Detroit, Michigan, USA

Posted: Mon Aug 21, 2006 1:04 am Post subject: Standardize? 


Tracy,
You are correct. I don't think a boxbox interaction is something different to learn. I also did not understand the Sadman explanation when I originally found it. I thought I was stupidly missing something.
Also, I'd like to see more standard terminology. I tried to impose one on myself:
"Box" not "block" or "square"..
"Candidate" not "possibility".
(Box  Line) "Interaction" not "intersection".
"Line" not "row or column".
"Naked single" not "forced square".
"Cell" not "square".
"Hidden single" not "pinned square".
It's tougher than I thought, to consistently use one set of terms.
By the way, my wife's cousins were here from Kalamazoo for (a family reunion and) the Woodward Dream Cruise this weekend. In just a few years, the Cruise has become an incredible event and spectacle.
Best wishes,
Keith 

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