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Apr 14 VH

 
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ZeroAssoluto



Joined: 05 Feb 2017
Posts: 868
Location: Rimini, Italy

PostPosted: Thu Apr 14, 2022 9:04 am    Post subject: Apr 14 VH Reply with quote

Hi everyone,

Code:

+--------------+-------------+--------------+
| 4    67  3   | 27  1   26  | 5   8    9   |
| 678  678 9   | 47  456 456 | 1   2    3   |
| 5    1   2   | 8   9   3   | 6   4    7   |
+--------------+-------------+--------------+
| 39   5   48  | 34  2   1   | 489 7    6   |
| 237  237 148 | 6   34  9   | 48  15   125 |
| 269  269 14  | 5   8   7   | 49  3    12  |
+--------------+-------------+--------------+
| 1238 238 5   | 9   36  268 | 7   16   4   |
| 1389 4   7   | 13  356 568 | 2   1569 15  |
| 129  29  6   | 124 7   245 | 3   159  8   |
+--------------+-------------+--------------+

Play this puzzle online at the Daily Sudoku site

Quote:
XY-Wing 1,3,6 in r7c58,r8c4 and -1 in r8c89
or
XY-Chain r5c8-1-r7c8-6-r7c5-3-r8c4-1-r8c9 and -5 in r5c9,r89c8


Ciao Gianni
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TomC



Joined: 30 Oct 2020
Posts: 349
Location: Wales

PostPosted: Thu Apr 14, 2022 9:55 am    Post subject: Reply with quote

Code:

+--------------+--------------+--------------+
| 4    67  3   | 27  1    26  | 5   8    9   |
| 678  678 9   | 47  456  456 | 1   2    3   |
| 5    1   2   | 8   9    3   | 6   4    7   |
+--------------+--------------+--------------+
| 39   5   48  | 34  2    1   | 489 7    6   |
| 237  237 148 | 6   34b  9   | 48  15a  125 |
| 269  269 14  | 5   8    7   | 49  3    12  |
+--------------+--------------+--------------+
| 1238 238 5   | 9   36c  268 | 7   16d   4  |
| 1389 4   7   | 13  356  568 | 2   1569  15 |
| 129  29  6   | 124 7    245 | 3   159   8  |
+--------------+--------------+--------------+

If a=1 then <48> pair in row 5 gives b=3, c=6 and d is also 1
so a must be 5
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Thu Apr 14, 2022 12:40 pm    Post subject: Reply with quote

In Eureka is:

(5=1)r5c8-(1=48)r5c37-(4=3)r5c5-(3=6)r7c5-(6=1)r7c8-(1=5)r5c8

R5c8 < > 1; stte
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TomC



Joined: 30 Oct 2020
Posts: 349
Location: Wales

PostPosted: Thu Apr 14, 2022 12:50 pm    Post subject: Reply with quote

Thanks for the notation Mogulmeister, I struggle with eureka, but if you describe something I know then this helps a lot!

Interestingly, you can put any value in r5c3 containing <148> because it still shows r5c8 cannot be <1>
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dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Thu Apr 14, 2022 12:52 pm    Post subject: Reply with quote

TomC wrote:
Code:
+--------------+--------------+--------------+
| 4    67  3   | 27  1    26  | 5   8    9   |
| 678  678 9   | 47  456  456 | 1   2    3   |
| 5    1   2   | 8   9    3   | 6   4    7   |
+--------------+--------------+--------------+
| 39   5   48  | 34  2    1   | 489 7    6   |
| 237  237 148 | 6   34b  9   | 48  15a  125 |
| 269  269 14  | 5   8    7   | 49  3    12  |
+--------------+--------------+--------------+
| 1238 238 5   | 9   36c  268 | 7   16d   4  |
| 1389 4   7   | 13  356  568 | 2   1569  15 |
| 129  29  6   | 124 7    245 | 3   159   8  |
+--------------+--------------+--------------+

If a=1 then <48> pair in row 5 gives b=3, c=6 and d is also 1
so a must be 5

Hi Tom, I just wanted to mention that the sudoku expert Clement taught me to put the letters in the front so that they stand out a little bit better. (See the example below.) When you put the letters at the end, they sort of blend in with the candidates.
Code:

+--------------+---------------+---------------+
| 4    67  3   | 27   1    26  | 5    8    9   |
| 678  678 9   | 47   456  456 | 1    2    3   |
| 5    1   2   | 8    9    3   | 6    4    7   |
+--------------+---------------+---------------+
| 39   5   48  | 34   2    1   | 489  7    6   |
| 237  237 148 | 6   b34   9   | 48  a15  125  |
| 269  269 14  | 5    8    7   | 49   3    12  |
+--------------+---------------+---------------+
| 1238 238 5   | 9   c36   268 | 7   d16    4  |
| 1389 4   7   | 13   356  568 | 2    1569  15 |
| 129  29  6   | 124  7    245 | 3    159   8  |
+--------------+---------------+---------------+


Last edited by dongrave on Thu Apr 14, 2022 1:01 pm; edited 2 times in total
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Thu Apr 14, 2022 12:59 pm    Post subject: Reply with quote

I confess to using both over the years!
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TomC



Joined: 30 Oct 2020
Posts: 349
Location: Wales

PostPosted: Thu Apr 14, 2022 1:06 pm    Post subject: Reply with quote

Thanks dongrave, I see your point with the clarity
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dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Thu Apr 14, 2022 5:34 pm    Post subject: Reply with quote

TomC wrote:
Thanks for the notation Mogulmeister, I struggle with eureka, but if you describe something I know then this helps a lot!

Interestingly, you can put any value in r5c3 containing <148> because it still shows r5c8 cannot be <1>

I also struggled with Eureka until one day I had this 'Aha!' moment and no longer thought about 'strong' and 'weak' links and instead began thinking of '=' as 'is equal to' and '-' as 'is not equal to'.
So, in Mogulmeister's example (5=1)r5c8-(1=48)r5c37-(4=3)r5c5-(3=6)r7c5-(6=1)r7c8-(1=5)r5c8
I simply read it as 'If r5c8 is equal to 1, then r5c37 are not 1 so they're 4 and 8, so r5c5 is not 4 so it's 3, so r7c5 is not 3 so it's 6, etc.
I saw someone explain this same approach not long ago on this site and I think that if more people were aware of this trick they'd have an easier time with Eureka!
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Fri Apr 15, 2022 5:59 am    Post subject: Reply with quote

Well remembered dongrave!

Mogulmeister wrote:
...and of course it is a chain as well.

(-1)r7c5=(1)r3c5-r3c9=(1)r8c9 so r8c4<>1

In English:

"It isn't 1 at r7c5 so must be 1 at r3c5 isn't 1 at r3c9 must be 1 at r8c9".

The logic always alternates between the " - "(isn't) to "=" (must be).

Usually there is a bracketed number or numbers just to the left of the cell reference to let you know what is going on. The above example is simple as we are only on digit 1. Where there is no bracketed number the chain assumes you are still on the same digit. I didn't really need the (1) quite so much above.

You will see in some of the more involved chains that there is a transition to another digit as in the example below:

(1=4)r4c2-(4=3)r8c2 etc

In English:

"Not 1 but must be 4 in r4c2 so not 4 but must be 3 in r8c2 etc"

This is for when you move from one strong linked digit to a different one.
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Fri Apr 15, 2022 10:15 am    Post subject: Reply with quote

TomC wrote:


Interestingly, you can put any value in r5c3 containing <148> because it still shows r5c8 cannot be <1>


Triple proof - nice !
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dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Sat Apr 16, 2022 9:21 pm    Post subject: Reply with quote

Mogulmeister wrote:
Well remembered dongrave!

Mogulmeister wrote:
...and of course it is a chain as well.

(-1)r7c5=(1)r3c5-r3c9=(1)r8c9 so r8c4<>1

In English:

"It isn't 1 at r7c5 so must be 1 at r3c5 isn't 1 at r3c9 must be 1 at r8c9".

The logic always alternates between the " - "(isn't) to "=" (must be).

Usually there is a bracketed number or numbers just to the left of the cell reference to let you know what is going on. The above example is simple as we are only on digit 1. Where there is no bracketed number the chain assumes you are still on the same digit. I didn't really need the (1) quite so much above.

You will see in some of the more involved chains that there is a transition to another digit as in the example below:

(1=4)r4c2-(4=3)r8c2 etc

In English:

"Not 1 but must be 4 in r4c2 so not 4 but must be 3 in r8c2 etc"

This is for when you move from one strong linked digit to a different one.


Aha! So that was you Mogulmeister?! From a post last year? I wish that people like me could buy books written by you - or Clement - or Keith - or Marty when he was alive.
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