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VH+072617

 
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Wed Jul 26, 2017 6:07 am    Post subject: VH+072617 Reply with quote

Enjoy the puzzle.....



Code:

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

Play this puzzle online at the Daily Sudoku site

immpy
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Ajò Dimonios



Joined: 01 May 2017
Posts: 339
Location: Sassari Italy

PostPosted: Wed Jul 26, 2017 12:23 pm    Post subject: Reply with quote

Hi everyone
One step solution after basics.
Code:

+-------------+------------+--------------+
| 47 28  1    | 6   5   9  | 247  478  3  |
| 9  6   2478 | 478 1   3  | 2457 4578 45 |
| 5  3   478  | 2   48  47 | 6    1    9  |
+-------------+------------+--------------+
| 2  47  3    | 5   479 6  | 8    49   1  |
| 6  1   45   | 48  489 2  | 3    459  7  |
| 8  457 9    | 3   47  1  | 45   6    2  |
+-------------+------------+--------------+
| 1  9   6    | 47  2   8  | 457  3    45 |
| 3  45  457  | 1   6   47 | 9    2    8  |
| 47 28  28   | 9   3   5  | 1    47   6  |
+-------------+------------+--------------+

Play this puzzle online at the Daily Sudoku site

Forcing chain [(5-7)R7C7=(7-4)R9C8=(4)R9C1 and (5)R7C7-(5)R6C7=(5)R6C2-(5=4)R8C2]=>contradiction two 4 singles in box 7=>-5R7C7 =>stte.
Ciao a tutti
Paolo
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Ajò Dimonios



Joined: 01 May 2017
Posts: 339
Location: Sassari Italy

PostPosted: Wed Jul 26, 2017 1:24 pm    Post subject: Reply with quote

Hi everyone
Another one step solution after basics.
Code:

+-------------+------------+--------------+
| 47 28  1    | 6   5   9  | 247  478  3  |
| 9  6   2478 | 478 1   3  | 2457 4578 45 |
| 5  3   478  | 2   48  47 | 6    1    9  |
+-------------+------------+--------------+
| 2  47  3    | 5   479 6  | 8    49   1  |
| 6  1   45   | 48  489 2  | 3    459  7  |
| 8  457 9    | 3   47  1  | 45   6    2  |
+-------------+------------+--------------+
| 1  9   6    | 47  2   8  | 457  3    45 |
| 3  45  457  | 1   6   47 | 9    2    8  |
| 47 28  28   | 9   3   5  | 1    47   6  |
+-------------+------------+--------------+

Play this puzzle online at the Daily Sudoku site

Forcing chain [(5)R2C9-(5)R2C8=(5)R5C8-(5)R5C3 and (5)R2C9-(5)R2C7=(5)R6C7-(5)R6C2=(5-4)R5C3]=>contradiction R5C3=Ø =>-5R2C9 =>stte.


Ciao a tutti
Paolo
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JC Van Hay



Joined: 13 Jun 2010
Posts: 494
Location: Charleroi, Belgium

PostPosted: Wed Jul 26, 2017 6:13 pm    Post subject: Reply with quote

15 singles; r19c2.r9c3=28; 4 singles
The solutions of the 4s exclude {4r2c78, 4r7c7}
... Interpretation : X-Loop{4R19C9}
The solutions of the 7s exclude {7r1c7, 7r2c38, 7r3c5, 7r8c2}
... Interpretation : Pointings{7B45}, X-Chain{7C14B9}

The solutions of {(45)r6c7, (57)r7c7, (74)r9c8} exclude {4r45c8}; stte
... Interpretation : XY-Wing
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Ajò Dimonios



Joined: 01 May 2017
Posts: 339
Location: Sassari Italy

PostPosted: Wed Jul 26, 2017 9:57 pm    Post subject: Reply with quote

Hi everyone
Another one step solution after basics.
Code:

+-------------+------------+--------------+
| 47 28  1    | 6   5   9  | 247  478  3  |
| 9  6   2478 | 478 1   3  | 2457 4578 45 |
| 5  3   478  | 2   48  47 | 6    1    9  |
+-------------+------------+--------------+
| 2  47  3    | 5   479 6  | 8    49   1  |
| 6  1   45   | 48  489 2  | 3    459  7  |
| 8  457 9    | 3   47  1  | 45   6    2  |
+-------------+------------+--------------+
| 1  9   6    | 47  2   8  | 457  3    45 |
| 3  45  457  | 1   6   47 | 9    2    8  |
| 47 28  28   | 9   3   5  | 1    47   6  |
+-------------+------------+--------------+

Play this puzzle online at the Daily Sudoku site

Forcing chain
[(5)R5C3-(5)R5C8=NP(49)R45C8-(4=7)R9C8 and (5)R5C3-(5)R5C8=(5)R2C8-(5=4)R2C9-(4)R1C78=(4-7)R1C1=(7)R9C1]=>contradiction two singles 7 in R9 =>-5R5C3 =>stte.


Ciao a tutti
Paolo
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Thu Jul 27, 2017 1:08 pm    Post subject: Reply with quote

Here, as promised from my previous puzzle posting, is the case where a Unique Rectangle will not work, because it occurs in four boxes, instead of two.
Notice the 47 in rows 1 and 9, columns 1 and 8. There is an extra candidate (8) in r1c8. If this were a true UR the 8 could be placed in this slot, but because the UR occurs (in this instance) in four boxes, it results in a contradiction. This means that the 8 cannot occur in r1c8.
Once that 8 is eliminated, the puzzle quickly solves with basics from there.

The first time I ran into this (in a previous puzzle long ago) I was dumbfounded when the usually reliable UR resulted in a contradiction. And the underlying reason was the occurrence of the UR in four boxes, as opposed to two. Chalked it up to another learning experience when it comes to Sudoku solving.

Hoping this example enlightens others.

immpy
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Ajò Dimonios



Joined: 01 May 2017
Posts: 339
Location: Sassari Italy

PostPosted: Thu Jul 27, 2017 3:14 pm    Post subject: Reply with quote

Hi Immpy

Immpy wrote:

Quote:
Here, as promised from my previous puzzle posting, is the case where a Unique Rectangle will not work, because it occurs in four boxes, instead of two.
Notice the 47 in rows 1 and 9, columns 1 and 8. There is an extra candidate ( 8 ) in r1c8. If this were a true UR the 8 could be placed in this slot, but because the UR occurs (in this instance) in four boxes, it results in a contradiction. This means that the 8 cannot occur in r1c8.
Once that 8 is eliminated, the puzzle quickly solves with basics from there.

The first time I ran into this (in a previous puzzle long ago) I was dumbfounded when the usually reliable UR resulted in a contradiction. And the underlying reason was the occurrence of the UR in four boxes, as opposed to two. Chalked it up to another learning experience when it comes to Sudoku solving.

Hoping this example enlightens others.


Immpy I fully agree with you that lines 1 and 8 do not form a Unique Rectangle because, as you have said correctly, it is placed in four boxes. I do not agree that this logically excludes the 8 in R1C8. In this case, it is a coincidence created by the double fin-xwing of 4 and 7 in the four cells (R1C1, R1C8, R9C8 and R9C1) which eliminates all the remaining 4 and 7 in columns 1 and 8 and lines 1 and 9. By this reason (hidden pair) the 8 in R1C8 must be eliminated.

Ciao a Tutti
Paolo
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Fri Jul 28, 2017 2:06 pm    Post subject: Reply with quote

Indeed yes, Paolo, your reasoning is spot-on and that is the correct way of applying the Non UR technique. It all ended up the same in this case, but I shall be more mindful of this in the future.
But I just have to ask....if the 8 cannot go there, why not just eliminate it as a candidate?

Thank you Paolo....

immpy
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Ajò Dimonios



Joined: 01 May 2017
Posts: 339
Location: Sassari Italy

PostPosted: Fri Jul 28, 2017 4:48 pm    Post subject: Reply with quote

Hi Immpy

Immpy. The fact that in this case UR technique can not be applied, because the vertices of the unique rectangle are placed on four boxes, it does not make any decision on candidate 8 positioned in the R1C8 cell. This means that it may be true or false. To be eliminated, it is necessary to demonstrate falsehood by applying a logic technique. Only using the trials and errors technique together with an x-wing can prove the false of 8 in R1C8.


p.s. I do not know the Non Unique rectangle technique.

Ciao a Tutti

Paolo
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Sat Jul 29, 2017 1:00 pm    Post subject: Reply with quote

The Non Unique Rectangle is not really a technique that one could or should know, it is just the name I gave to it because it is NOT a Unique Rectangle (because of the four box occurrence).

Totally agree with you on the logic sequencing for this instance.

My next posted puzzle will bring up something even more baffling (at least for me, anyway).

Stay tuned.....


Thank you Paolo...

immpy
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immpy



Joined: 06 May 2017
Posts: 570

PostPosted: Tue Aug 01, 2017 4:53 pm    Post subject: Reply with quote

Please disregard my comment concerning my next posted puzzle. I discovered why I was baffled; the puzzle had multiple solutions so I scrapped it.

But I HAVE posted a new puzzle, which is legit.

Thanks all,

immpy
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