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Jun 20 VH

 
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ZeroAssoluto



Joined: 05 Feb 2017
Posts: 941
Location: Rimini, Italy
PostPosted: Sun Jun 20, 2021 9:34 am    Post subject: Jun 20 VH Reply with quote
Hi everyone,

Code:

+---------+-------+-----------+
| 9 4  5  | 1 7 3 | 6  2   8  |
| 7 3  8  | 6 2 4 | 9  1   5  |
| 6 1  2  | 5 8 9 | 37 347 47 |
+---------+-------+-----------+
| 3 89 6  | 4 5 7 | 1  89  2  |
| 1 78 4  | 2 9 6 | 57 578 3  |
| 5 2  79 | 8 3 1 | 4  79  6  |
+---------+-------+-----------+
| 2 79 1  | 3 4 5 | 8  6   79 |
| 8 6  39 | 7 1 2 | 35 345 49 |
| 4 5  37 | 9 6 8 | 2  37  1  |
+---------+-------+-----------+

Play this puzzle online at the Daily Sudoku site

Quote:
W-Wing 3,7 in r3c7,r9c8 SL with number 7 in r37c9 and -3 in r3c8,r8c7
or
XY-Wing 3,5,7 in r58c7,r9c8 and -7 in r56c8


Ciao Gianni
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TomC



Joined: 30 Oct 2020
Posts: 358
Location: Wales
PostPosted: Sun Jun 20, 2021 9:53 am    Post subject: Reply with quote
The 357 wing that Gianni describes can also be used to remove the 7 in r9c3 as this leads to no 7's in box 4
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Mogulmeister



Joined: 03 May 2007
Posts: 1151
PostPosted: Mon Jun 21, 2021 8:59 am    Post subject: Reply with quote
TomC wrote:
The 357 wing that Gianni describes can also be used to remove the 7 in r9c3 as this leads to no 7's in box 4.


Yes - this can be extended via the (79)r6c8 to (79)r6c3 to create a slightly longer xy-chain which means that one of the pincers at r6c3 or r9c8 must be 7 ==> -7 at r9c3 and r6c8.

A good illustration showing that underneath these wing structures lurk the building blocks or fundamental xy chains.


The 37 W Wing is an XY chain too. One of those pincers at r3c7 or r9c8 must be 3 ==> -3 at r8c7 and r3c8.

Here's the notation which shows all this.

If you plug in "not 3" eg 7 at r3c7 you still get 3 in r9c8

(3=7)r3c7-(7=4)r3c9-(4=9)r8c9-(9=7)r7c9-(7=3)r9c8

If you plug in "not 3" eg 7 at r9c8 you still get 3 in r3c7

(3=7)r9c8-(7=9)r7c9-(9=4)r8c9-(4=7)r3c9-(7=3)r3c7
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