dailysudoku.com Forum Index dailysudoku.com
Discussion of Daily Sudoku puzzles
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Puzzle 10/7/31 A

 
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Puzzles by daj
View previous topic :: View next topic  
Author Message
dejsmith



Joined: 23 Oct 2005
Posts: 42
PostPosted: Tue Aug 03, 2010 5:51 pm    Post subject: Puzzle 10/7/31 A Reply with quote
Danny, sorry to be behind & that is why I am not broadcasting this. But I do not understand an apparent contradiction I see in the Kraken/Almost X Wing Peterj presented. Using ttt's candidate profiles, Peterj's route to include r7c8<>7 makes sense. But, if you take the route from r1c7=7 to r8c7=8, then you get the opposite that r7c8=7? That is why when I applied this Kraken/Almost X Wing, I only made eliminations in r23c8. How do you account for this apparent contradiction in r7c8? What am I not understanding?

Thanks...Dave
Back to top
View user's profile Send private message
daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Tue Aug 03, 2010 11:48 pm    Post subject: Reply with quote
Hello Dave, I'm always glad to help. Let's hope that I succeed in this case.

Here is the grid used by peterj. I'll start at the beginning, but I believe your answer will be at the end.

Code:
 +-----------------------------------------------------------------------+
 |  14     9      5      | *14678  168    2      | @478   *1678   3      |
 |  2      1478   147    |  14678  3      678    |  4789   1689-7 5      |
 |  3      1478   6      |  1478   9      5      |  2      18-7   78     |
 |-----------------------+-----------------------+-----------------------|
 |  146    146    9      |  3      2      678    |  178    5      78     |
 |  8      5      2      | *79     4      1      |  3     *79     6      |
 |  7      16     3      |  689    5      68     |  189    4      2      |
 |-----------------------+-----------------------+-----------------------|
 |  146    2      147    |  168    168    3      |  5      8-7    9      |
 |  5      167    17     |  2      168    9      |  78     3      4      |
 |  9      3      8      |  5      7      4      |  6      2      1      |
 +-----------------------------------------------------------------------+
 # 71 eliminations remain

1) For <7>, either the (*) cells are true for the X-Wing or else cell (@) r1c7 is true.

2) If the (*) cells are true, then r23c4<>7 and r237c8<>7.

3) The (@) cell is a fin cell and a finned X-Wing exists for r23c8<>7.

However, peterj was greedy and wanted r237c8<>7. So, he decided to pursue a Kraken X-Wing instead of accepting the finned X-Wing. This meant that he needed a chain from r1c7 to r5c8 ... and he found it. Now, here's where your quandry fits into the picture.

4a) If you start with a true assumption, then everything that follows must be true. This is half of what makes true/false (conjugate) logic work.

4b) It you start with a false assumption, then nothing can be said for certain about what follows.

4c) What makes conjugate logic work is the overlapping of the conclusions from the conjugate starting points. You no longer need to know which assumption is true/false, only that the false assumption leads to some conclusions in common with the true assumption.

Peter found a chain that had three eliminations in common with the X-Wing -- r237c8<>7. Your chain found two eliminations in common with the X-Wing -- r23c8<>7. In the case of this puzzle, assuming r1c7=7 happens to be a false assumption -- for your chain and peterj's chain. So, recalling (4b), it's no surprise that the results of your chain differed from peterj's chain. Okay?

===== ===== ===== ===== =====

An example of false assumption logic in the real world.

False Assumption -> False Conclusion: (7)r1c7 - (7)r1c8

False Assumption -> True Conclusion: (7)r1c7 - (7)r1c4

Regards, Danny
Back to top
View user's profile Send private message
dejsmith



Joined: 23 Oct 2005
Posts: 42
PostPosted: Wed Aug 04, 2010 12:41 am    Post subject: Reply with quote
Thanks Danny. I'll start paying more attention to everyone's posts about Krakens. I must admit my solving techniques have always aligned closer to Marty's; and I probably take the cake for MOST steps required; but I really enjoy your puzzles & everyones' comments. Because of you guys, I am broadening out, & trying to learn & apply some of these new (for me) techniques.

Dave
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Puzzles by daj All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group