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ZeroAssoluto
Joined: 05 Feb 2017
Posts: 940
Location: Rimini, Italy
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 Posted: Wed Nov 03, 2021 10:14 am Post subject: Nov 03 VH |
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Hi everyone,
| Code: |
+------------+-----------------+---------------+
| 6 3 49 | 2789 5 1 | 48 2489 78 |
| 49 8 1 | 279 6 249 | 345 2349 57 |
| 5 7 2 | 3 49 489 | 1 489 6 |
+------------+-----------------+---------------+
| 7 46 5 | 19 139 39 | 468 468 2 |
| 2 9 3 | 4 8 6 | 7 5 1 |
| 1 46 8 | 25 7 25 | 9 46 3 |
+------------+-----------------+---------------+
| 8 1 46 | 59 34 7 | 2 36 59 |
| 349 2 469 | 1589 1349 34589 | 3568 7 589 |
| 39 5 7 | 6 2 389 | 38 1 4 |
+------------+-----------------+---------------+
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Play this puzzle online at the Daily Sudoku site
First step X-Wing with number 8 in r18c49 and -8 in r1c78,r8c67
| Code: |
+----------+----------------+-------------+
| 6 3 9 | 78 5 1 | 4 2 78 |
| 4 8 1 | 279 6 29 | 35 39 57 |
| 5 7 2 | 3 49 489 | 1 89 6 |
+----------+----------------+-------------+
| 7 46 5 | 19 139 39 | 68 468 2 |
| 2 9 3 | 4 8 6 | 7 5 1 |
| 1 46 8 | 25 7 25 | 9 46 3 |
+----------+----------------+-------------+
| 8 1 46 | 59 34 7 | 2 36 59 |
| 39 2 46 | 1589 1349 3459 | 356 7 589 |
| 39 5 7 | 6 2 389 | 38 1 4 |
+----------+----------------+-------------+
|
Play this puzzle online at the Daily Sudoku site
Second step XY-Wing 3,6,8 in r49c7,r7c8 and -6 in r46c8,r8c7
OR with only one step AIC in r7c8
if r7c8=6 and -6 in r46c8,r8c7
if r7c8=3 r2c7=3 r8c7=5 r4c7=6 and -6 in r46c8,r8c7
Ciao Gianni |
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TomC
Joined: 30 Oct 2020
Posts: 358
Location: Wales
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| Posted: Wed Nov 03, 2021 10:46 am Post subject: |
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From the first grid position
UR <46> in r46c28 means r4c8 must be 8
or if r4c7= 8, r9c7=3, r7c8=6 gives no 6's in box 6 |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Wed Nov 03, 2021 12:07 pm Post subject: |
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| TomC wrote: |
or if r4c7= 8, r9c7=3, r7c8=6 gives no 6's in box 6 |
I believe this contradiction works after basics and not just after the first position, Tom.
You would, after basics, have two "not 6" conditions in r4c7 -> 8 or 4. You dealt with 8 above but what if you chose 4 ?
Well r4c7 = 4, r1c7 = 8, r9c7 = 3 and r7c8 = 6 which also gives no 6's in box 6.
This contradiction could be generally expressed as:
(6=48)r14c7-(8=3)r9c7-(3=6)r7c8-(6=48)r46c8-(48=6)r4c7
Take 6 out of r4c7 and the loop insists it must be 6 - which it is. |
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TomC
Joined: 30 Oct 2020
Posts: 358
Location: Wales
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| Posted: Wed Nov 03, 2021 12:40 pm Post subject: |
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| The way I saw it was if r4c7 can't be 8 then r4c8 must be 8 |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Wed Nov 03, 2021 12:59 pm Post subject: |
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Yes the flip side of r4c7 being 6 is that it is also not 8 so when you plug 8 into r4c7 you show it can't be there in the first place. Put it into the loop which evicts it.
(46=8)r4c7-(8=3)r9c7-(3=6)r7c8-(46=8)r46c8-(8)r4c7 ==> r4c8 = 8 |
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dongrave
Joined: 06 Mar 2014
Posts: 568
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| Posted: Wed Nov 03, 2021 3:04 pm Post subject: |
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| I used the 8 X -Wing as the 1st step and then the 356 XYZ-Wing with pivot at r8c7 (-3r9c7) as the 2nd step. |
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Mogulmeister
Joined: 03 May 2007
Posts: 1151
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| Posted: Thu Nov 04, 2021 1:50 pm Post subject: Re: Nov 03 VH |
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| ZeroAssoluto wrote: |
Second step XY-Wing 3,6,8 in r49c7,r7c8 and -6 in r46c8,r8c7
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You can have this as a slightly modified first step after basics where it is an Almost XY wing
468-38-36 there is a 4 in r4c7
If it is FALSE then we have the XY-wing as above.
If it is TRUE then (68=4)r4c7-(4=8)r1c7-(8=3)r9c7-(3=6)r7c8 and -6 in r46c8,r8c7 also. |
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