November 11, 2016

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November 11, 2016

Postby ArkieTech » Fri Nov 11, 2016 12:31 am

Code: Select all
 *-----------*
 |..9|...|1..|
 |.68|...|94.|
 |71.|...|.65|
 |---+---+---|
 |...|9.6|...|
 |...|518|...|
 |...|2.4|...|
 |---+---+---|
 |49.|...|.28|
 |.82|...|61.|
 |..7|...|4..|
 *-----------*


Play/Print this puzzle online
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Re: November 11, 2016

Postby SteveG48 » Fri Nov 11, 2016 12:37 am

Code: Select all
 *--------------------------------------------------------------------*
 | 235    345    9      | 6      48     37     | 1      378    237    |
 | 23     6      8      | 137    5      137    | 9      4      237    |
 | 7      1      34     | 48     29     29     | 38     6      5      |
 *----------------------+----------------------+----------------------|
 | 18     2347   345    | 9      37     6      |b23578  3578   14     |
 | 9      2347   346    | 5      1      8      |b237   a37     46     |
 | 18     37     56     | 2      37     4      | 58     9      16     |
 *----------------------+----------------------+----------------------|
 | 4      9      1      | 37     6      357    |c357    2      8      |
 | 35     8      2      | 347    49     3579   | 6      1     d37     |
 | 6      35     7      | 18     28     12     | 4      5-3    9      |
 *--------------------------------------------------------------------*


(3=7)r5c8 - r45c7 = r7c7 - (7=3)r8c9 => -3 r9c8 ; stte
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Re: November 11, 2016

Postby pjb » Fri Nov 11, 2016 1:20 am

Code: Select all
b235     345     9      | 6      48     37     | 1      378    237   
b23      6       8      | 137    5      137    | 9      4      237   
 7       1      a34     | 8-4     29     29     | 38     6      5     
------------------------+----------------------+---------------------
 18      2347    345    | 9      37     6      | 23578  3578   14     
 9       2347    346    | 5      1      8      | 237    37     46     
 18      37      56     | 2      37     4      | 58     9      16     
------------------------+----------------------+---------------------
 4       9       1      | 37     6      357    | 357    2      8     
c35      8       2      |d347    49     3579   | 6      1     d37     
 6       35      7      | 18     28     12     | 4      35     9     

(4=3)r3c3 - r12c1 = r8c1 - (3=4)r8c49 => -4 r3c4; stte

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Re: November 11, 2016

Postby Leren » Fri Nov 11, 2016 3:38 am

Code: Select all
*--------------------------------------------------------------*
| 235   345   9      | 6     48    37     | 1     378   237    |
| 23    6     8      | 137   5     137    | 9     4     237    |
| 7     1     34     | 48    29    29     | 38    6     5      |
|--------------------+--------------------+--------------------|
| 18    2347  345    | 9     37    6      |c23578 3578  14     |
| 9     2347  346    | 5     1     8      |c237  b37    46     |
| 18    37    56     | 2     37    4      | 58    9     16     |
|--------------------+--------------------+--------------------|
| 4     9     1      | 37    6     357    |d37-5  2     8      |
| 35    8     2      | 347   49    3579   | 6     1     37     |
| 6     35    7      | 18    28    12     | 4    a35    9      |
*--------------------------------------------------------------*

(5=3) r9c8 - (3=7) r5c8 - r45c7 = (7) r7c7 => - 5 r7c7; stte

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Re: November 11, 2016

Postby Sudtyro2 » Fri Nov 11, 2016 11:27 am

Code: Select all
*--------------------------------------------------------------*
| 235   345   9      | 6     48    37     | 1     378   237    |
| 23    6     8      | 137   5     137    | 9     4     237    |
| 7     1     34     | 48    29    29     | 38    6     5      |
|--------------------+--------------------+--------------------|
| 18    2347  345    | 9     37    6      | 23578 3578  14     |
| 9     2347  346    | 5     1     8      | 237   37    46     |
| 18    37    56     | 2     37    4      | 58    9     16     |
|--------------------+--------------------+--------------------|
|*4     9     1      | 37   *6     357    | 357   2     8      |
| 35    8     2      | 347  *9-4   3579   |*6     1     37     |
|*6     35    7      | 18    28    12     |*4     35    9      |
*--------------------------------------------------------------*
If I fully understand the concept...
The digits 4 and 6 in the six marked cells form a Reverse BUG-Lite.
This implies -4r8c5; stte
Edit to add: I did not fully understand the concept...
See subsequent discussions.

SteveC
Last edited by Sudtyro2 on Sat Nov 12, 2016 8:54 pm, edited 1 time in total.
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Re: November 11, 2016

Postby Ngisa » Fri Nov 11, 2016 5:09 pm

Code: Select all
+--------------+-------------+----------------+
| 235 g35-4 9   | 6   48 37   | 1     378  237 |
| 23  6    8   | 137 5  137  | 9     4    237 |
| 7   1    a34  | 48  29 29   | b38    6    5   |
+--------------+-------------+----------------+
| 18  2347 345 | 9   37 6    | 23578 d3578 14  |
| 9   2347 346 | 5   1  8    | 237   37   46  |
| 18  37   56  | 2   37 4    | c58    9    16  |
+--------------+-------------+----------------+
| 4   9    1   | 37  6  357  | 357   2    8   |
| 35  8    2   | 347 49 3579 | 6     1    37  |
| 6   f35   7   | 18  28 12   | 4     e35   9   |
+--------------+-------------+----------------+

(4=3)r3c3 - (3=8)r3c7 - (8=5)r6c7 - r4c8 = r9c8 - r9c2 = (5)r1c2 => -4 r1c2; stte

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Re: November 11, 2016

Postby Leren » Fri Nov 11, 2016 7:32 pm

Sudtyro2 wrote : The digits 4 and 6 in the six marked cells form a Reverse BUG-Lite.

I don't think that's right because some of the * cells are clues, so you couldn't get the reverse pattern in the solution if the * cells were fully exposed.

The pattern is like an Avoidable Rectangle with 6 cells. You can read the Hodoku comments on this topic here and Andew Stuart's comments here.

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Re: November 11, 2016

Postby Sudtyro2 » Fri Nov 11, 2016 8:18 pm

Leren wrote: I don't think that's right because some of the * cells are clues, so you couldn't get the reverse pattern in the solution if the * cells were fully exposed.

Thx, Leren, for the feedback. This is all a first shot for me, based mostly on older posts by RW.

Vidarino made that same comment about "givens" in the pattern, but RW, who I think originated the "reverse" Bug here: http://forum.enjoysudoku.com/uniqueness-chains-t3542.html#p23592, seems to refute that argument. His discussion clarifies some issues about "givens" and "solved" cells and then leads into the "Reverse" approach to Bug-Lites.

I also can't find mention of a non-givens requirement in his later post here:
http://forum.enjoysudoku.com/reverse-bug-lite-t4957.html#p36383. And, the Sudopedia Mirror article on Reverse BUG-Lites actually uses one of RW's 3-digit examples with no mention of givens.

I'll take a look at the Hodoku link and report back.

BTW, yesterday's puzzle (11/10/16) also has an apparent 6-cell reverse bug pattern in the top tier using the 9&3 digits. The elimination of 3r2c2 is proper, but doesn't lead to an stte solution that I could find. I didn't look at the givens in that puzzle.

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Re: November 11, 2016

Postby Leren » Fri Nov 11, 2016 8:52 pm

I had a look at RW's post and he says :
Code: Select all
1..|...|...
...|...|...
2..|1..|...
-----------
...|...|...
...|...|...
...|...|...
-----------
...|...|...
...|...|...
...|...|...

Assume these are the only given, or logically solved, instances of numbers 1 and 2 on the grid. If we placed number 2 in r1c4, then we would have two number pairs that can be defined by two rows (1 and 3) two columns (1 and 4) and 2 boxes (1 and 2). That means that in each other unit left on the grid there has to be exactly two spaces reserved for numbers 1 and 2, which in the end will lead to a bug => we can safely remove candidate 2 from r1c4.

My underlining of the word given. This statement, taken literally, Is wrong. If any of the 1's or 2 in the grid is actually a given, you absolutely cannot remove 2 from r1c4 due to a uniqueness argument. The reason is that you can't reverse the 1's and 2's in the 4 cells, because there are givens there. On the other hand, If none of the 1's or 2 is a given you can remove 2 from r1c4, because you could reverse the 1's and 2's in the 4 cells, for either 0 or 2 solutions.

As Andrew Stuart points out in his article, Avoidable Rectangles is the only move in Sudoku that requires you to remember which solved cells were clues and which were not. In fact, his first example in his article directly refutes RW's remarks.

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Last edited by Leren on Fri Nov 11, 2016 9:25 pm, edited 1 time in total.
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Re: November 11, 2016

Postby Sudtyro2 » Fri Nov 11, 2016 9:23 pm

Thx again, Leren, for the helpful feedback. I think I'll now defer to your assessments and study the suggested links (while licking my wounds). It did seem too easy, did it not?

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Re: November 11, 2016

Postby SteveG48 » Sat Nov 12, 2016 2:24 pm

Interesting discussion guys. I haven't figured out all the arguments in the cited postings, but it does seem that the problem with givens was resolved because the bug would appear someplace else (the "reverse" aspect). I hope this discussion continues.
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Re: November 11, 2016

Postby Sudtyro2 » Sat Nov 12, 2016 4:51 pm

Here's a quick follow-up in support of Leren's observations...

1. Two months before RW's post, Vidarino posted his work defining an Almost Unavoidable Set: http://forum.enjoysudoku.com/new-unique-pattern-trick-t3352.html. It's clear from his very first example grid that no givens can be present in the Almost pattern.

2. Today's (11/12/16) puzzle grid seems to have a potential 4-cell Reverse BUG-Lite in (46)r27c89 that would require -4r2c9 to avoid the BUG. However, +4r2c9 is the correct solution, and 6r2c8 is a given.

Somehow, Vidarino and I both completely misunderstood RW's arguments about the givens. I do, however, believe the Reverse BUG-Lite would work fine without any givens. I'll be checking future puzzles for those (probably rare) cases. Added: Upon a careful reread, I think Vidarino did fully understand RW's arguments.
Thx again to Leren for the enlightening feedback.

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Last edited by Sudtyro2 on Sun Nov 13, 2016 7:00 pm, edited 1 time in total.
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Re: November 11, 2016

Postby SteveG48 » Sat Nov 12, 2016 5:39 pm

It's the part about the givens that I don't understand. RW argues that the unavoidable BUG will occur elsewhere even if the solved BUG pattern includes givens. I don't follow the argument. It does occur to me that a counterexample might be found. If RW's argument is correct, then there will be no valid (unique solution) Sudokus in for which the solution includes a simple unique rectangle with one or more givens. Can anyone come up with such a puzzle?

The part about the givens is crucial. If we conclude that RW's argument is wrong, then the reverse BUG idea, while interesting, does us no good. In this puzzle, your argument deleting the 4 would be perfectly valid as an ordinary BUG lite solution if the pattern didn't contain givens.
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Re: November 11, 2016

Postby JasonLion » Sat Nov 12, 2016 6:55 pm

Every solution grid has deadly rectangles if you assume that none of the cells are clues. (As far as I can tell. I haven't proved it. If it isn't every grid, then it is nearly every grid.) The basic pattern of a deadly rectangle is quite common. A puzzle creator needs to make sure (one way or another) that every deadly rectangle present in the solution grid has at least one clue in it (which kills the deadly rectangle).

I'm certain that RW didn't mean clue when he said "given". Not sure what he did mean, but it wasn't clue. Perhaps he meant cell you have already figured out. Hard to say for sure.
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Re: November 11, 2016

Postby SteveG48 » Sat Nov 12, 2016 7:56 pm

Thanks, Jason. That clarifies things. Now that you mention it, this puzzle (11/11) has a 2/7 UR at r57c78 with a given 2 at r7c8. RW must have meant something else.
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