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May 21 VH

 
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ZeroAssoluto



Joined: 05 Feb 2017
Posts: 632
Location: Rimini, Italy

PostPosted: Fri May 21, 2021 9:01 am    Post subject: May 21 VH Reply with quote

Hi everyone,

Code:

+-----------+--------+-----------+
| 79  1  79 | 8 2 5  | 6  3   4  |
| 6   2  5  | 4 3 7  | 9  8   1  |
| 8   4  3  | 9 1 6  | 7  25  25 |
+-----------+--------+-----------+
| 49  7  49 | 1 5 2  | 8  6   3  |
| 25  3  1  | 6 8 4  | 25 7   9  |
| 25  6  8  | 3 7 9  | 4  1   25 |
+-----------+--------+-----------+
| 34  59 2  | 7 6 1  | 35 459 8  |
| 1   89 6  | 5 4 38 | 23 29  7  |
| 347 58 47 | 2 9 38 | 1  45  6  |
+-----------+--------+-----------+

Play this puzzle online at the Daily Sudoku site

Quote:
XY-Wing 3,4,5 in r7c17,r9c8 and -4 in r7c8,r9c13
or
XYZ-Wing 4,5,9 in r7c28,r9c8 and -5 in r7c7


Ciao Gianni
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TomC



Joined: 30 Oct 2020
Posts: 107
Location: Wales

PostPosted: Fri May 21, 2021 12:11 pm    Post subject: Reply with quote

Another way to solve (not sure of name) is r9c8 <> 5

otherwise r9c2 = 8, r8c2 = 9, r8c8 = 2 and gives r3c8 also = 5

Tom
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Mogulmeister



Joined: 03 May 2007
Posts: 868

PostPosted: Tue Jun 22, 2021 1:18 pm    Post subject: Reply with quote

TomC wrote:
Another way to solve (not sure of name) is r9c8 <> 5

otherwise r9c2 = 8, r8c2 = 9, r8c8 = 2 and gives r3c8 also = 5

Tom


a)When 5 is input into a loop at r9c8, the loop looks to remove that 5 therefore the 5 can be eliminated because it is a contradiction (also a 5 in the same column). Sometimes called a discontinuous nice loop! You can also get the reverse of this when you remove a number from a square and the loop tries to reinsert that number - which means it belongs there.

What you have also described Tom is (for me) most simply seen as:

b)XY-chain - your pincers for 5 are at the ends of your chain in r3c8 and r9c2 - one of these is 5 and so r9c8 <> 5.
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