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Puzzle 11/02/08 Obtuse

 
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Tue Feb 08, 2011 4:36 pm    Post subject: Puzzle 11/02/08 Obtuse Reply with quote
Would you believe an XY-Chain using half of the exposed bivalue cells?

Code:
 +-----------------------+
 | . . 8 | . . . | . . 2 |
 | . . . | . . 6 | . . . |
 | 6 . 9 | 2 1 . | . . . |
 |-------+-------+-------|
 | . . 4 | 6 . 9 | . 7 . |
 | . . 6 | . 7 . | . 5 9 |
 | . 8 . | 3 . . | . . 6 |
 |-------+-------+-------|
 | . . . | . . . | 6 8 4 |
 | . . . | 8 3 . | 1 . . |
 | 8 . . | . 6 5 | 7 . . |
 +-----------------------+

Play this puzzle online at the Daily Sudoku site
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peterj



Joined: 26 Mar 2010
Posts: 974
Location: London, UK
PostPosted: Tue Feb 08, 2011 5:23 pm    Post subject: Reply with quote
Yes. Fortunately one end of it started on row1 so I didn't have to go check them all...

I thought this was a nice one-step hidden-pair move...
Quote:
hp(57)r12c4=(7)r13c6 - (7=4)r8c5 - (4=9)r9c4 ; r12c4<>9
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Wed Feb 09, 2011 6:02 am    Post subject: Reply with quote
I played a worthless ER on 8. Then the potential DP on 59 in boxes 23 yielded numerous common outcomes from the DP killers.
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Wed Feb 09, 2011 3:00 pm    Post subject: Reply with quote
I posted this puzzle because I couldn't believe the XY-Chain that cracks it.

Code:
 after basics
 +-----------------------------------------------------------------------+
 |  13457  13457  8      |  579    49    a37     |  459    6      2      |
 |  23457  23457  35     |  579    489    6      |  4589   134    178    |
 |  6      3457   9      |  2      1      78-3   |  458   h34     78     |
 |-----------------------+-----------------------+-----------------------|
 |  1235   1235   4      |  6     e28     9      |  238    7     f18     |
 |  123    123    6      |  14     7      1248   |  2348   5      9      |
 |  9      8      7      |  3      5      124    |  24    g14     6      |
 |-----------------------+-----------------------+-----------------------|
 |  357    3579   35     |  179   d29     127    |  6      8      4      |
 |  47     6      2      |  8      3     b47     |  1      9      5      |
 |  8      49     1      | c49     6      5      |  7      2      3      |
 +-----------------------------------------------------------------------+
 # 82 eliminations remain

(3=7)r1c6 (=4)r8c6 (=9)r9c4 (=2)r7c5 (=8)r4c5 (=1)r4c9 (=4)r6c8 (=3)r3c8  =>  r3c6<>3
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ronk



Joined: 07 May 2006
Posts: 398
PostPosted: Wed Feb 09, 2011 4:26 pm    Post subject: Reply with quote
daj95376 wrote:
I posted this puzzle because I couldn't believe the XY-Chain that cracks it.
(3=7)r1c6 (=4)r8c6 (=9)r9c4 (=2)r7c5 (=8)r4c5 (=1)r4c9 (=4)r6c8 (=3)r3c8 => r3c6<>3

Keep whacking away at the AIC notation ... and you'll soon have NL notation. Smile

Quote:
r3c6 -3- r1c6 -7- r8c6 -4- r9c4 -9- r7c5 -2- r4c5 -8- r4c9 -1- r6c8 -4- r3c8 -3- r3c6
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Wed Feb 09, 2011 7:44 pm    Post subject: Reply with quote
ronk wrote:
daj95376 wrote:
I posted this puzzle because I couldn't believe the XY-Chain that cracks it.
(3=7)r1c6 (=4)r8c6 (=9)r9c4 (=2)r7c5 (=8)r4c5 (=1)r4c9 (=4)r6c8 (=3)r3c8 => r3c6<>3

Keep whacking away at the AIC notation ... and you'll soon have NL notation. Smile

Quote:
r3c6 -3- r1c6 -7- r8c6 -4- r9c4 -9- r7c5 -2- r4c5 -8- r4c9 -1- r6c8 -4- r3c8 -3- r3c6

I gave up on NL notation quite awhile back. I just haven't committed to reducing Eureka notation to my satisfaction:

Quote:
3=7r1c6 4r8c6 9r9c4 2r7c5 8r4c5 1r4c9 4r6c8 3r3c8; r3c6<>3

(Yes, I know this has been done.)

Have you considered updating NL notation?

Quote:
r3c6 =3- r1c6 =7- r8c6 =4- r9c4 =9- r7c5 =2- r4c5 =8- r4c9 =1- r6c8 =4- r3c8 =3- r3c6

(Yes, I recall that this doesn't work in some instances.)
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ronk



Joined: 07 May 2006
Posts: 398
PostPosted: Wed Feb 09, 2011 8:17 pm    Post subject: Reply with quote
daj95376 wrote:
Have you considered updating NL notation?
Quote:
r3c6 =3- r1c6 =7- r8c6 =4- r9c4 =9- r7c5 =2- r4c5 =8- r4c9 =1- r6c8 =4- r3c8 =3- r3c6

(Yes, I recall that this doesn't work in some instances.)

What does '=x-' mean anyway? Whatever it means, it doesn't look to read properly both left-to-right and right-to-left. If that's true, I wouldn't be interested.
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daj95376



Joined: 23 Aug 2008
Posts: 3854
PostPosted: Wed Feb 09, 2011 10:55 pm    Post subject: Reply with quote
ronk wrote:
What does '=x-' mean anyway? Whatever it means, it doesn't look to read properly both left-to-right and right-to-left. If that's true, I wouldn't be interested.

Is a chain any less true if you only read it from left-to-right? Myth Jellies' comment about AICs being bidirectional (seems to me) is more anecdotal than conditional. Do you have an example where reading a chain -- AIC or NL -- from right-to-left is necessary?
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ronk



Joined: 07 May 2006
Posts: 398
PostPosted: Thu Feb 10, 2011 2:04 am    Post subject: Reply with quote
daj95376 wrote:
ronk wrote:
What does '=x-' mean anyway? Whatever it means, it doesn't look to read properly both left-to-right and right-to-left. If that's true, I wouldn't be interested.

Is a chain any less true if you only read it from left-to-right? Myth Jellies' comment about AICs being bidirectional (seems to me) is more anecdotal than conditional. Do you have an example where reading a chain -- AIC or NL -- from right-to-left is necessary?

If one is satisfied with what is then unquestionably elimination-by-contradiction (EBC), bidirectionality is not required. Personally, I don't find EBC satisfying.
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