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c.v.fr. 24/03/2019

 
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Aj Dimonios



Joined: 01 May 2017
Posts: 338
Location: Sassari Italy

PostPosted: Sat Mar 23, 2019 10:30 pm    Post subject: c.v.fr. 24/03/2019 Reply with quote

Hi everyone



Code:

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

Play this puzzle online at the Daily Sudoku site

apparently easy but not so.

Ciao a Tutti
Paolo
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immpy



Joined: 06 May 2017
Posts: 236

PostPosted: Mon Mar 25, 2019 2:01 am    Post subject: Reply with quote

Another BRUTAL puzzle, Paolo. You may consider me thoroughly STUMPED!

cheers...immp
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Aj Dimonios



Joined: 01 May 2017
Posts: 338
Location: Sassari Italy

PostPosted: Wed Mar 27, 2019 10:32 am    Post subject: Reply with quote

Hi everyone.
After basics
Code:

+------------+-------------+----------------+
| 569 1 5689 | 2569 7  3   | 4    2569 5689 |
| 3   7 5689 | 2569 29 4   | 2589 1    5689 |
| 569 4 2    | 8    1  569 | 7    569  3    |
+------------+-------------+----------------+
| 7   3 569  | 569  8  2   | 1    569  4    |
| 4   2 569  | 1    3  569 | 589  7    5689 |
| 569 8 1    | 7    4  569 | 359  3569 2    |
+------------+-------------+----------------+
| 8   9 4    | 23   5  1   | 6    23   7    |
| 12  6 7    | 239  29 8   | 235  4    15   |
| 12  5 3    | 4    6  7   | 29   8    19   |
+------------+-------------+----------------+

Play this puzzle online at the Daily Sudoku site
Five step after basics.
This scheme is a classic example that can be solved using the technique Naked Sets http://www.philsfolly.net.au/naked_help.htm.
It can be used in line 3 or 4. In these sets there are three cells that have 569 as candidates. The possible combinations that solve the pattern are 6 but 5 lead to a contradiction while the last leads to the solution using only the technique of basis. I report the conclusions of the combinations that lead to contradiction for the case of line 3.
R3C1=5, R3C6=6 e R3C8=9
R9C7=

Code:

+--------+----------+----------+
| 9  1 8 | 25  7  3 | 4  6 5   |
| 3  7 6 | 59  9  4 | 2  1 58  |
| 5  4 2 | 8   1  6 | 7  9 3   |
+--------+----------+----------+
| 7  3 9 | 6   8  2 | 1  5 4   |
| 4  2 5 | 1   3  9 | 8  7 6   |
| 6  8 1 | 7   4  5 | 9  3 2   |
+--------+----------+----------+
| 8  9 4 | 23  5  1 | 6  2 7   |
| 12 6 7 | 239 29 8 | 35 4 159 |
| 12 5 3 | 4   6  7 | .  8 19  |
+--------+----------+----------+

Play this puzzle online at the Daily Sudoku site
R3C1=5, R3C6=9 e R3C8=6
R5C3=
Code:

+---------+--------+------------+
| 6  1 89 | 5  7 3 | 4   29 589 |
| 3  7 89 | 6  2 4 | 589 1  589 |
| 5  4 2  | 8  1 9 | 7   6  3   |
+---------+--------+------------+
| 7  3 6  | 9  8 2 | 1   5  4   |
| 4  2 .  | 1  3 5 | 89  7  6   |
| 9  8 1  | 7  4 6 | 3   3  2   |
+---------+--------+------------+
| 8  9 4  | 23 5 1 | 6   23 7   |
| 12 6 7  | 23 9 8 | 235 4  15  |
| 12 5 3  | 4  6 7 | 29  8  19  |
+---------+--------+------------+

Play this puzzle online at the Daily Sudoku site
R3C1=6, R3C6=5 e R3C8=9
R9C7=
Code:

+--------+----------+----------+
| 9  1 8 | 26  7  3 | 4  5 6   |
| 3  7 5 | 69  9  4 | 2  1 68  |
| 6  4 2 | 8   1  5 | 7  9 3   |
+--------+----------+----------+
| 7  3 9 | 5   8  2 | 1  6 4   |
| 4  2 6 | 1   3  9 | 58 7 58  |
| 5  8 1 | 7   4  6 | 9  3 2   |
+--------+----------+----------+
| 8  9 4 | 23  5  1 | 6  2 7   |
| 12 6 7 | 239 29 8 | 35 4 159 |
| 12 5 3 | 4   6  7 | .  8 19  |
+--------+----------+----------+

Play this puzzle online at the Daily Sudoku site.
R3C1=6, R3C6=9 e R3C8=5
R5C9=
Code:

+--------+-------+---------+
| 5  1 8 | 6 7 3 | 4  9 8  |
| 3  7 9 | 5 2 4 | 8  1 6  |
| 6  4 2 | 8 1 9 | 7  5 3  |
+--------+-------+---------+
| 7  3 5 | 9 8 2 | 1  6 4  |
| 4  2 6 | 1 3 5 | 9  7 .  |
| 9  8 1 | 7 4 6 | 5  3 2  |
+--------+-------+---------+
| 8  9 4 | 2 5 1 | 6  3 7  |
| 12 6 7 | 3 9 8 | 25 4 15 |
| 12 5 3 | 4 6 7 | 2  8 19 |
+--------+-------+---------+

Play this puzzle online at the Daily Sudoku site
R3C1=9, R3C6=5 e R3C8=6
R6C7=
Code:

+---------+----------+-------------+
| 6  1 58 | 29  7  3 | 4    25 589 |
| 3  7 58 | 6   29 4 | 2589 1  589 |
| 9  4 2  | 8   1  5 | 7    6  3   |
+---------+----------+-------------+
| 7  3 6  | 5   8  2 | 1    9  4   |
| 4  2 .  | 1   3  9 | 58   7  6   |
| 5  8 1  | 7   4  6 | .    3  2   |
+---------+----------+-------------+
| 8  9 4  | 23  5  1 | 6    2  7   |
| 12 6 7  | 239 29 8 | 2359 4  159 |
| 12 5 3  | 4   6  7 | 29   8  19  |
+---------+----------+-------------+

Play this puzzle online at the Daily Sudoku site
R3C1=9, R3C6=6 e R3C8=5=>solution.

Ciao a Tutti
Paolo
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immpy



Joined: 06 May 2017
Posts: 236

PostPosted: Wed Mar 27, 2019 12:36 pm    Post subject: Reply with quote

Naked sets, eh? OK, I see the logic. Of course, someone might call this guessing (not myself).
My program WAS able to whittle this puzzle down to a point where one could use the Finned XY-Wing as a means to a solution, which is another technique that gets categorized as "guessing" by some. The pertinent cell was r8c7 with the "fin" of 3 either being true or false. The "fin" in this case proved true with no contradictions, so r8c7=3.

The fin was in the pivot cell of a 235 XY-Wing. 35 was located at r6c7 and 23 was located at r7c8. Thus cell r8c7 is either <> 3 (=25!) or the fin of 3 is true for this cell.

cheers...imp

Still a damn tough puzzle which I could not solve without help.
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Aj Dimonios



Joined: 01 May 2017
Posts: 338
Location: Sassari Italy

PostPosted: Wed Mar 27, 2019 1:21 pm    Post subject: Reply with quote

Hi Immpy,
Immpy Wrote:

Code:
 Naked sets, eh? OK, I see the logic. Of course, someone might call this guessing (not myself).
My program WAS able to whittle this puzzle down to a point where one could use the Finned XY-Wing as a means to a solution, which is another technique that gets categorized as "guessing" by some. The pertinent cell was r8c7 with the "fin" of 3 either being true or false. The "fin" in this case proved true with no contradictions, so r8c7=3.

The fin was in the pivot cell of a 235 XY-Wing. 35 was located at r6c7 and 23 was located at r7c8. Thus cell r8c7 is either <> 3 (=25!) or the fin of 3 is true for this cell.

Frankly, I think the term "guess" should only be used in cases where the solution is found without demonstrating its uniqueness. In this case all Backdoors (R1C4 = 2, R1C8 = 6, R2C5 = 9, R2C7 = 2, R6C7 = 5, R7C8 = 3, R7C4 = 3, R7C8 = 2, R8C5 = 2 and R8C7 = 3) and all resolutions in which obviously a priori techniques of uniqueness are used (uniqueness1-2-3-4-5-6,Hidden rectangle e avoidable rectangle 1-2).In practice I think that useful techniques should only be based on logics that demonstrate a contradiction.

Ciao a Tutti
Paolo
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immpy



Joined: 06 May 2017
Posts: 236

PostPosted: Thu Mar 28, 2019 12:22 pm    Post subject: Reply with quote

I agree wholeheartedly, my friend...just relating the sentiment I often encounter when I use the Finned XY-Wing to solve on occasion. Maybe Naked Sets will be more accepted by our solving peers.

cheers...immp
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Aj Dimonios



Joined: 01 May 2017
Posts: 338
Location: Sassari Italy

PostPosted: Thu Mar 28, 2019 1:29 pm    Post subject: Reply with quote

Hi Immpy,
Immpy Wrote:
Code:
I agree wholeheartedly, my friend...just relating the sentiment I often encounter when I use the Finned XY-Wing to solve on occasion. Maybe Naked Sets will be more accepted by our solving peers



The difference between the two methods is this: finxyWind allows you to find a solution to the scheme, identifying a backdoor R8C7 = 3, but it does not allow you to demonstrate its uniqueness, which is generally the most difficult operation, in this case it takes 5 step to do it. I believe that a complete resolution must also contain this passage.

Ciao a Tutti
Paolo
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