There Was a Time: 03/29/13

Post puzzles for others to solve here.

There Was a Time: 03/29/13

Postby daj95376 » Fri Mar 29, 2013 8:46 am

There was a time when I use to post puzzles.

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


Play this puzzle online at the Daily Sudoku site
daj95376
2014 Supporter
 
Posts: 2624
Joined: 15 May 2006

Re: There Was a Time: 03/29/13

Postby ArkieTech » Fri Mar 29, 2013 12:01 pm

I remember fondly :D

Code: Select all
 *--------------------------------------------------------------------*
 | 346    46     7      | 1234   1238   9      | 24     5      12348  |
 | 34     1      8      | 5      23     6      | 9      7      234    |
 | 5      9      2      | 134    1378   478    | 6      348    1348   |
 |----------------------+----------------------+----------------------|
 | 2468   46     13     | 9      1268   48     | 5      34     7      |
 | 24     5      9      | 234    237    47     | 8      1      6      |
 | 68     7      13     | 14     68     5      | 24     9      234    |
 |----------------------+----------------------+----------------------|
 | 9      2      6      | 7      5      3      | 1      48     48     |
 | 7      8      4      | 6      9      1      | 3      2      5      |
 | 1      3      5      | 8      4      2      | 7      6      9      |
 *--------------------------------------------------------------------*
net
2r1c7-r1c4=r5c4-(2=4)r5c1-r2c1=r2c9-r7c9=4r7c8
||
4r1c7-----------r3c8
     -r1c2=r4c2-r4c8=4r7c8 => 4r7c8; ste
dan
User avatar
ArkieTech
 
Posts: 2678
Joined: 29 May 2006
Location: NW Arkansas USA

Re: There Was a Time: 03/29/13

Postby JC Van Hay » Fri Mar 29, 2013 7:07 pm

Interpretations of Dan's solution ...

1. Colouring C7 with the complementary colours a,A gives
    a : r6c7,r5c1,r1c4=2 and r1c7,r4c1,r1c2=4
    A : r1c7,r5c4=2 and r6c7,r5c1,r1c2,r2c9=4
    a=A :=> -2r1c59,-2r5c5 and -4r1c149,-4r3c89,-4r4c18
or
Code: Select all
+-----------------+---------------------+---------------------+
| 36-4   6(4A) 7  | 13-4(2a) 138-2  9   | (2A4a) 5     138-24 |
| 3(4a)  1     8  | 5        23     6   | 9      7     23(4A) |
| 5      9     2  | 134      1378   478 | 6      38-4  138-4  |
+-----------------+---------------------+---------------------+
| 268-4  6(4a) 13 | 9        1268   48  | 5      3-4   7      |
| (2a4A) 5     9  | 34(2A)   37-2   47  | 8      1     6      |
| 68     7     13 | 14       68     5   | (2a4A) 9     234    |
+-----------------+---------------------+---------------------+
| 9      2     6  | 7        5      3   | 1      48    48     |
| 7      8     4  | 6        9      1   | 3      2     5      |
| 1      3     5  | 8        4      2   | 7      6     9      |
+-----------------+---------------------+--------------------+
2. Chain[6] : WRing{(4=2)r1c7-2r1c4=2r5c4-(2=4)r5c1-4r4c2=4r1c2}-[4r2c1=4r2c9 and (2=4)r6c7]
    WR :=> -2r1c59,-2r5c5,-4r4c1,-4r1c149
    4r1c7=4r2c9 :=> -4r3c89
    4r4c2=4r6c7 :=> -4r4c8 [equivalent to Skyscraper(4C27)]
Therefore, r7c8=8;stte
JC Van Hay
 
Posts: 713
Joined: 22 May 2010

Re: There Was a Time: 03/29/13

Postby Marty R. » Sat Mar 30, 2013 4:41 am

Code: Select all
 *--------------------------------------------------------------------*
 | 346    46     7      | 1234   1238   9      | 24     5      12348  |
 | 34     1      8      | 5      23     6      | 9      7      234    |
 | 5      9      2      | 134    1378   478    | 6      348    1348   |
 |----------------------+----------------------+----------------------|
 | 2468   46     13     | 9      1268   48     | 5      34     7      |
 | 24     5      9      | 234    237    47     | 8      1      6      |
 | 68     7      13     | 14     68     5      | 24     9      234    |
 |----------------------+----------------------+----------------------|
 | 9      2      6      | 7      5      3      | 1      48     48     |
 | 7      8      4      | 6      9      1      | 3      2      5      |
 | 1      3      5      | 8      4      2      | 7      6      9      |
 *--------------------------------------------------------------------*


Two steps.

W-Wing (24) + transport (4=2)r1c7-r1c4=r5c4-(2=4)r5c1-r12c1=r1c2=>r1c149<>4
Skyscraper, c27=>r4c8<>4
Marty R.
 
Posts: 1430
Joined: 23 October 2012
Location: Rochester, New York, USA

Re: There Was a Time: 03/29/13

Postby David P Bird » Sat Mar 30, 2013 11:54 am

Code: Select all
 *-------------------*---------------------*-------------------*
 |  346  h46   7     | 1234  a1238   9     | 24    5     2348  |
 | g34    1    8     | 5      23     6     | 9     7    f234   |
 |  5     9    2     | 134   b1378  b47-8  | 6    c348   1348  |
 *-------------------*---------------------*-------------------*
 |  2468 i46   13    | 9      126-8 j48    | 5     34    7     |
 |  24    5    9     | 234    237    47    | 8     1     6     |
 |  68    7    13    | 14     6-8    5     | 24    9     234   |
 *-------------------*---------------------*-------------------*
 |  9     2    6     | 7      5      3     | 1    d48   e48    |
 |  7     8    4     | 6      9      1     | 3     2     5     |
 |  1     3    5     | 8      4      2     | 7     6     9     |
 *-------------------*---------------------*-------------------*


Just (4)s and (8)s

(8)r1c5 = (8)r3c56 - (8)r3c8 = (8-4)r7c8 = (4)r7c9 - (4)r2c9 = (4)r2c1 - (4)r1c2 = (4)r4c2 - (4=8)r4c6
=> r3c6,r46c5 <> 8 sste
David P Bird
2010 Supporter
 
Posts: 960
Joined: 16 September 2008
Location: Middle England

Re: There Was a Time: 03/29/13

Postby Luke » Sat Mar 30, 2013 3:41 pm

ArkieTech wrote:I remember fondly :D

Code: Select all
 *--------------------------------------------------------------------*
 | 346    46     7      | 1234   1238   9      | 24     5      12348  |
 | 34     1      8      | 5      23     6      | 9      7      234    |
 | 5      9      2      | 134    1378   478    | 6      348    1348   |
 |----------------------+----------------------+----------------------|
 | 2468   46     13     | 9      1268   48     | 5      34     7      |
 | 24     5      9      | 234    237    47     | 8      1      6      |
 | 68     7      13     | 14     68     5      | 24     9      234    |
 |----------------------+----------------------+----------------------|
 | 9      2      6      | 7      5      3      | 1      48     48     |
 | 7      8      4      | 6      9      1      | 3      2      5      |
 | 1      3      5      | 8      4      2      | 7      6      9      |
 *--------------------------------------------------------------------*
net
2r1c7-r1c4=r5c4-(2=4)r5c1-r2c1=r2c9-r7c9=4r7c8
||
4r1c7-----------r3c8
     -r1c2=r4c2-r4c8=4r7c8 => 4r7c8; ste


Isn't this what's known as "bifurcation"?
User avatar
Luke
2015 Supporter
 
Posts: 435
Joined: 06 August 2006
Location: Southern Northern California

Re: There Was a Time: 03/29/13

Postby ArkieTech » Sat Mar 30, 2013 5:08 pm

Luke451 wrote:
Code: Select all
2r1c7-r1c4=r5c4-(2=4)r5c1-r2c1=r2c9-r7c9=4r7c8
||
4r1c7-----------r3c8
     -r1c2=r4c2-r4c8=4r7c8 => 4r7c8; ste

Isn't this what's known as "bifurcation"?


I don't know. I am still in "learning mode".
dan
User avatar
ArkieTech
 
Posts: 2678
Joined: 29 May 2006
Location: NW Arkansas USA

Re: There Was a Time: 03/29/13

Postby JC Van Hay » Sat Mar 30, 2013 5:59 pm

ArkieTech wrote:
Luke451 wrote:
Code: Select all
2r1c7-r1c4=r5c4-(2=4)r5c1-r2c1=r2c9-r7c9=4r7c8
||
4r1c7-----------r3c8
     -r1c2=r4c2-r4c8=4r7c8 => 4r7c8; ste

Isn't this what's known as "bifurcation"?


I don't know. I am still in "learning mode".
No, AFAICT, Dan's chain is a "dynamic forcing chain" due to the "4r1c7-4r3c8" allowing, with -4r4c8, =4r7c8 (memory effect).
Notes : in the interpretations I gave of Dan's solution, I replaced the SISs 4C8+4R7 by (24)r6c7. Furthermore, as it is well clear from Marty's solution, the W-Ring and the Skyscraper are all that is needed to solve this puzzle!
JC Van Hay
 
Posts: 713
Joined: 22 May 2010

Re: There Was a Time: 03/29/13

Postby daj95376 » Sat Mar 30, 2013 7:04 pm

From Jeff's definitions, I interpret a network to be a forcing chain where secondary/memory eliminations are used to reach the final conclusion. Dan's solution matches my usage.

I tried calling it a Kraken Cell, but ronk insisted that term only applied to cells containing three or more candidates. As for other terms, I thought that it also worked as a Double-Implication Chain, but I believe that usage applied to bilocation and not bivalue. Besides, Sudopedia updated the definition of Double-Implication Chain and my usage was called the "old way".

As for my solver's solutions to this puzzle, I favor/chose the following:

Code: Select all
 after basics
 +-----------------------------------------------------------------------+
 |  346   *46     7      |  1234   1238   9      | *24     5      12348  |
 |  34     1      8      |  5      23     6      |  9      7      234    |
 |  5      9      2      |  134    1378   478    |  6      348    1348   |
 |-----------------------+-----------------------+-----------------------|
 |  2468  *46     13     |  9      1268   48     |  5      3-4    7      |
 |  24     5      9      |  234    237    47     |  8      1      6      |
 |  68     7      13     |  14     68     5      | *24     9      234    |
 |-----------------------+-----------------------+-----------------------|
 |  9      2      6      |  7      5      3      |  1      48     48     |
 |  7      8      4      |  6      9      1      |  3      2      5      |
 |  1      3      5      |  8      4      2      |  7      6      9      |
 +-----------------------------------------------------------------------+
 # 55 eliminations remain

 c27r1   Skyscraper                      <> 4    r4c8

 after additional basics
 +--------------------------------------------------------------+
 |  346  a46    7     |  23-4  18    9     |  24    5     18    |
 |  34    1     8     |  5     23    6     |  9     7     234   |
 |  5     9     2     | e34    178   78    |  6     48    1348  |
 |--------------------+--------------------+--------------------|
 |  2468 b46    1     |  9     268   48    |  5     3     7     |
 | c24    5     9     | d23    237   47    |  8     1     6     |
 |  68    7     3     |  1     68    5     |  24    9     24    |
 |--------------------+--------------------+--------------------|
 |  9     2     6     |  7     5     3     |  1     48    48    |
 |  7     8     4     |  6     9     1     |  3     2     5     |
 |  1     3     5     |  8     4     2     |  7     6     9     |
 +--------------------------------------------------------------+
 # 38 eliminations remain

 XY-Chain:  (4=6)r1c2 - (6=4)r4c2 - (4=2)r5c1 - (2=3)r5c4 - (3=4)r3c4  =>  r1c4<>4

 -or-

 S-Wing:    (2)r1c4 = r5c4 - (2=4)r5c1 - r4c2 = (4)r1c2  =>  r1c4<>4


According to the Sudopedia Mirror on this site, the definition of Bifurcation involves a contradiction for one candidate forcing a strongly-linked (companion) candidate to be true. That's definitely not the outcome in Dan's solution.
daj95376
2014 Supporter
 
Posts: 2624
Joined: 15 May 2006

Re: There Was a Time: 03/29/13

Postby Luke » Sat Mar 30, 2013 8:13 pm

JC Van Hay wrote:No, AFAICT, Dan's chain is a "dynamic forcing chain" due to the "4r1c7-4r3c8" allowing, with -4r4c8, =4r7c8 (memory effect).

I'm guessing that bifurcation is distinguished from a forcing chain. Bifurcation is choosing one of the two candidates of a bivalue cell and following it along either to a solution or a contradiction. A forcing chain follows each in turn until a common outcome is reached. How does that sound as a simplification?

Either way seems unattractive to me, unless I'm missing something.
User avatar
Luke
2015 Supporter
 
Posts: 435
Joined: 06 August 2006
Location: Southern Northern California

Re: There Was a Time: 03/29/13

Postby daj95376 » Sat Mar 30, 2013 9:35 pm

Luke451 wrote:
JC Van Hay wrote:No, AFAICT, Dan's chain is a "dynamic forcing chain" due to the "4r1c7-4r3c8" allowing, with -4r4c8, =4r7c8 (memory effect).

I'm guessing that bifurcation is distinguished from a forcing chain. Bifurcation is choosing one of the two candidates of a bivalue cell and following it along either to a solution or a contradiction. A forcing chain follows each in turn until a common outcome is reached. How does that sound as a simplification?

Either way seems unattractive to me, unless I'm missing something.

I've been chastized severely in the past for saying that I believe that an AIC and a specific forcing chain structure are equivalent. On that note, please pretend that I didn't say the following:

Forcing Chain version of Skyscraper elimination:

Code: Select all
(4)r6c7                      - (4)r4c8
(4)r6c7 = r1c7 - r1c2 = r4c2 - (4)r4c8

The forcing chain says that the two possible states for <4> in r6c7 lead to a common outcome; r4c8<>4.

AIC/X-Chain version of Skyscraper:

Code: Select all
(4)r6c7 = r1c7 - r1c2 = r4c2  =>  r4c8<>4

For the AIC, r4c8=4 forces both ends of the chain false ... so it can be eliminated.

You say TOE-MAY-TOE and I say toe-may-toe.
daj95376
2014 Supporter
 
Posts: 2624
Joined: 15 May 2006

Re: There Was a Time: 03/29/13

Postby Marty R. » Sat Mar 30, 2013 9:48 pm

You say TOE-MAY-TOE and I say toe-may-toe.


Doesn't one of you say toe-MAH-toe? :lol:
Marty R.
 
Posts: 1430
Joined: 23 October 2012
Location: Rochester, New York, USA

Re: There Was a Time: 03/29/13

Postby DonM » Sat Mar 30, 2013 10:32 pm

(Please assume that IMO is at the beginning of every paragraph :))

This discussion is another indication as to how much has been lost with the complete wiping out of the Eureka forum. I feel like I'm living in a sudoku parallel universe where issues are being discussed as if they are new (where they were put to bed long ago) and methods that were long ago put in their place are being resurrected as if something new to use alongside more credible manual-solving methods (for a given puzzle difficulty).

Fwiw, the original Players' Forum gave us the gift of so many basic and advanced solving methods, but Eureka gave of us the gift of advanced manual solving and the best approaches to it. (Of course, there was cross-pollination between the two forums.) Around 2007, we had many discussions on the issues of assumptivity and bifurcation. (These discussions included some of the best manual solvers and math theorists.)

There was a lot of disagreement over what, in hindsight, appeared to be minutiae, but there was a general consensus over what was considered to be highly assumptive where assumptiveness generally refers to the level of assumptions made (ie. very close to, if not, guessing) used in a given method or in the overall approach to solving.

I used to refer to methods or patterns as either being 'what is' or 'what may be'. The least assumptive methods were 'what is' patterns such as naked pairs, x-wings, xy-wings and the like. All you had to do was recognize them and you could assume the result. When it came to chains/AICs, the 'what is' patterns could include simple chains based on transport. If one found an xy-wing and used transport to create a wider chain, then, again, the result spoke for itself.

However, as puzzles being solved became more difficult, more assumptive methods had to be developed and so you had the addition of various 'almost' patterns and finally, the use of AAICs (almost-AICs, unfortunately also called Kraken cell/row/column) and the like.

Part of the above discussion involved the premise of 'elegant' solving which partly means using the least assumptive methods for a puzzle as possible. That generally includes reserving the use of most nets for the most difficult puzzles (ie. somewhere around above ER=8.3). I don't think there's anything wrong with using nets for simpler puzzles if one is simply trying to learn how to use them- I did a lot of that in 2007- but once learned, I think that the real challenge of sudoku is to be an elegant solver: use simple methods for simple puzzles (which most of the puzzles in the section are) and reserve nets and the like for puzzles that deserve them.

During the same time there were these discussions and a lot of advanced manual solving on Eureka, there was a separate UK forum sub-section where the overall solving method was known as bifurcation or bifurcating. Generally, this always involved variations of making assumptions about what the value of a cell might be, particularly by splitting bivalue cells, and seeing where that leads. I never saw any change/improvement in the few methods that were used there and the process always seemed the same. Inevitably, variations of what are, by any measure that I know of, forcing chains (as a method-see below) would be used.

One can try to put lipstick on a pig by quoting definitions of forcing chains as found in the very old threads of Jeff (et al) where forcing chains were discussed generically and the term 'double-implication chain' was also used as a description, but the fact is that the use of forcing chains as a method as described here (http://www.sudokuassistant.co.uk/solving/solving-sudoku-forcing-chains.htm) is by any measure that I know of, bifurcating! And if one doesn't want to get their arms around that then forcing chains and/or splitting bivalue cells is highly assumptive compared to, say, a simple transport-derived chain.

PS. IMO, there are exceptions to the premise that nets are in the 'what may be' or more assumptive category. Examples of those exceptions are Empty Rectangles and Broken Wings-based solutions expressed as chains. The chains may inevitably be net-like, but the patterns are 'what is' patterns and the results are 'what is'.
DonM
2013 Supporter
 
Posts: 475
Joined: 13 January 2008

Re: There Was a Time: 03/29/13

Postby daj95376 » Sun Mar 31, 2013 8:36 pm

DonM wrote:(Please assume that IMO is at the beginning of every paragraph :))

.... I feel like I'm living in a sudoku parallel universe where issues are being discussed as if they are new (where they were put to bed long ago) and methods that were long ago put in their place are being resurrected as if something new to use alongside more credible manual-solving methods (for a given puzzle difficulty).

Yes, the discussions at the Eureka forum are lost ... and they weren't for everyone even when they existed. Learn to live with it!

BTW, congratulations on finding a link to the worst explanation of forcing chains that I've ever encountered! The site ever reversed cell locations by using [column,row]. Nice going DonM !!!
daj95376
2014 Supporter
 
Posts: 2624
Joined: 15 May 2006

Re: There Was a Time: 03/29/13

Postby DonM » Mon Apr 01, 2013 1:40 am

daj95376 wrote:
DonM wrote:(Please assume that IMO is at the beginning of every paragraph :))

.... I feel like I'm living in a sudoku parallel universe where issues are being discussed as if they are new (where they were put to bed long ago) and methods that were long ago put in their place are being resurrected as if something new to use alongside more credible manual-solving methods (for a given puzzle difficulty).

Yes, the discussions at the Eureka forum are lost ... and they weren't for everyone even when they existed. Learn to live with it!

I'll try Dr. Freud. Still, you might have a different perspective on the subject at hand if you had taken a little time out from programming to follow some of those discussions.

BTW, congratulations on finding a link to the worst explanation of forcing chains that I've ever encountered! The site ever reversed cell locations by using [column,row]. Nice going DonM !!!


I'm sorry that that example didn't work for you. Here are a number of others that appear to use the same (according to you 'worst') explanations. The forcing chain method as described in them is the same one I used when I started solving in late 2005. Even when I read Jeff's generic definition of forcing chains I was able to distinguish it from the forcing chain 'method'.

http://www.sudokuoftheday.com/pages/techniques-10.php
http://www.sadmansoftware.com/sudoku/forcingchain.htm
http://www.intosudoku.com/Doc/ForcingChain.html
http://www.sudoku129.com/puzzles/tips_44.php
http://sudoku.awardspace.biz/solving_sudoku_advanced.php?technique_id=Forcing%20chain
DonM
2013 Supporter
 
Posts: 475
Joined: 13 January 2008

Next

Return to Puzzles