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Dec 28 VH

 
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ZeroAssoluto



Joined: 05 Feb 2017
Posts: 685
Location: Rimini, Italy

PostPosted: Tue Dec 28, 2021 10:46 am    Post subject: Dec 28 VH Reply with quote

Hi everyone,

Code:

+-----------+------------+--------+
| 7  3  49  | 49  8  6   | 5 1 2  |
| 6  5  8   | 1   3  2   | 7 4 9  |
| 2  49 1   | 7   59 459 | 3 8 6  |
+-----------+------------+--------+
| 59 7  2   | 8   4  59  | 1 6 3  |
| 3  49 459 | 59  6  1   | 2 7 8  |
| 8  1  6   | 3   2  7   | 4 9 5  |
+-----------+------------+--------+
| 45 2  57  | 6   1  8   | 9 3 47 |
| 1  6  79  | 459 59 3   | 8 2 47 |
| 49 8  3   | 2   7  49  | 6 5 1  |
+-----------+------------+--------+

Play this puzzle online at the Daily Sudoku site

Quote:
Remote Pair 4,9 r5c2,r3c2,r1c3,r1c4 and -9 in r5c4
or
W-Wing
4,9 in r1c4,r9c6 SL with number 9 in r38c5 and -4 in r3c6,r8c4
5,9 in r3c5,r5c4 SL with number 5 in r8c45 and -9 in r1c4
4,9 in r3c2,r9c6 SL with number 9 in r38c5 and -4 in r3c6
4,9 in r1c4,r5c2 SL with number 4 in r3c26 and -9 in r5c4
5,9 in r4c6,r8c5 SL with number 5 in r3c56 and -9 in r9c6


Ciao Gianni
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TomC



Joined: 30 Oct 2020
Posts: 227
Location: Wales

PostPosted: Tue Dec 28, 2021 11:39 am    Post subject: Reply with quote

Using standard moves

X wing on <9> r49 removes 9 from r3c6
then XY wing <459> removes 5 from r3c5
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TomC



Joined: 30 Oct 2020
Posts: 227
Location: Wales

PostPosted: Tue Dec 28, 2021 12:51 pm    Post subject: Reply with quote

Or you could say r9c6 <> 9 as then r3c6 = 4, r1c4 = 9 leads to no <9>'s in box 5
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Mogulmeister



Joined: 03 May 2007
Posts: 1136

PostPosted: Tue Dec 28, 2021 2:38 pm    Post subject: Reply with quote

TomC wrote:
Using standard moves

X wing on <9> r49 removes 9 from r3c6
then XY wing <459> removes 5 from r3c5


Your almost XY wing starts out life with the extra 9 in r3c6.
If that 9 were true then there would be no 9ís in row 4 so we can dispense with it and the xy wing is true.
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TomC



Joined: 30 Oct 2020
Posts: 227
Location: Wales

PostPosted: Tue Dec 28, 2021 2:52 pm    Post subject: Reply with quote

If r3c6 was 9 then there would be no 9's in row 4 and no 9's in row 9 as well

Is that different to an X wing?
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Mogulmeister



Joined: 03 May 2007
Posts: 1136

PostPosted: Tue Dec 28, 2021 4:19 pm    Post subject: Reply with quote

The result is the same as the x wing but the logic is different as is the start point for 9 at r3c6 and it forces a contradiction.

The x wing is not about contradictions and we donít know which of the vertices are +9 or -9 just that one is true and the other is false which is enough to eliminate the 9 at r3c6.

One is contradictory the other is not.
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