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May 21 VH

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ZeroAssoluto

Joined: 05 Feb 2017
Posts: 941
Location: Rimini, Italy

Posted: Fri May 21, 2021 9:01 am Post subject: May 21 VH

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

TomC

Joined: 30 Oct 2020
Posts: 358
Location: Wales

Posted: Fri May 21, 2021 12:11 pm Post subject:

Another way to solve (not sure of name) is r9c8 <> 5 otherwise r9c2 = 8, r8c2 = 9, r8c8 = 2 and gives r3c8 also = 5 Tom

Mogulmeister

Joined: 03 May 2007
Posts: 1151

Posted: Tue Jun 22, 2021 1:18 pm Post subject:

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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