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ZeroAssoluto
Joined: 05 Feb 2017
Posts: 940
Location: Rimini, Italy
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 Posted: Sun Feb 25, 2018 11:24 pm Post subject: Feb 26 VH |
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Hi everyone,
| Code: |
+-----------+----------------+--------------+
| 23 9 5 | 6 18 18 | 23 4 7 |
| 1 4 8 | 2 379 379 | 369 69 5 |
| 23 6 7 | 4 359 359 | 8 1 29 |
+-----------+----------------+--------------+
| 4 5 12 | 78 6 1789 | 29 289 3 |
| 6 7 9 | 3 58 2 | 4 58 1 |
| 8 12 3 | 159 4 159 | 2569 7 269 |
+-----------+----------------+--------------+
| 9 23 4 | 78 23578 3578 | 1 256 26 |
| 7 123 6 | 15 1235 4 | 259 259 8 |
| 5 8 12 | 19 129 6 | 7 3 4 |
+-----------+----------------+--------------+
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Play this puzzle online at the Daily Sudoku site
| Quote: | | XY-Wing 2,6,9 in r2c8,r37c9 and -6 in r7c8 |
Ciao Gianni |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Mon Feb 26, 2018 5:57 am Post subject: |
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| Code: | ┌───────────────────────┬───────────────────────┬───────────────────────┐
│ 23 9 5 │ 6 18 18 │ 23 4 7 │
│ │ │ │
│ 1 4 8 │ 2 379 379 │ 369 69 5 │
│ │ │ │
│ 23 6 7 │ 4 359 359 │ 8 1 29 │
├───────────────────────┼───────────────────────┼───────────────────────┤
│ 4 5 12 │ 78 6 1789 │ 29 289 3 │
│ │ │ │
│ 6 7 9 │ 3 58 2 │ 4 58 1 │
│ │ │ │
│ 8 12 3 │ 159 4 159 │ 2569 7 269 │
├───────────────────────┼───────────────────────┼───────────────────────┤
│ 9 23 4 │ 78 23578 3578 │ 1 256 26 │
│ │ │ │
│ 7 123 6 │ 15 1235 4 │ 259 259 8 │
│ │ │ │
│ 5 8 12 │ 19 129 6 │ 7 3 4 │
└───────────────────────┴───────────────────────┴───────────────────────┘ |
UR (29) r48c78
8r4c8=5r8c78
8r4c8-(8=5)r5c8-5r7c8
5r8c78-5r7c8=> -5r7c8 |
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immpy
Joined: 06 May 2017
Posts: 571
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| Posted: Mon Feb 26, 2018 4:22 pm Post subject: |
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| Nice touch Marty...avoiding the 2-69 XY-wing. Beautiful. |
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dongrave
Joined: 06 Mar 2014
Posts: 568
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| Posted: Tue Feb 27, 2018 12:55 am Post subject: |
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| immpy wrote: | | Nice touch Marty...avoiding the 2-69 XY-wing. Beautiful. |
Hey! What happened? I remember when Marty would not use a UR to solve a problem on this site! And neither would Keith - so I said to myself, I said 'Don' I said, I said 'I will not use anything except wings to solve VH's on this site!'  (btw, I used the 29-6 XY wing to solve it.) |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue Feb 27, 2018 2:44 am Post subject: |
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| Quote: |
Hey! What happened? I remember when Marty would not use a UR to solve a problem on this site! |
Absolutely correct, Don. I've evolved and changed my approach to these puzzles, mostly avoiding the X, XY and XYZ wings. |
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Ajò Dimonios
Joined: 01 May 2017
Posts: 339
Location: Sassari Italy
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| Posted: Tue Feb 27, 2018 8:22 am Post subject: |
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Hi everyone
Dongrave wrote:
| Quote: |
Hey! What happened? I remember when Marty would not use a UR to solve a problem on this site!
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In fact, the use of the UR method is not appreciated by the sudoku community because it does not demonstrate the uniqueness of the solution. If we accept as correct the use of the UR method we will also have to accept the "back-door" solutions, which, as the UR does not demonstrate the uniqueness of the solution, as correct. Let me explain with this example in this puzzle R2C8 = 6 "back-door" is a puzzle solution without proof of uniqueness while
[9R2C8- (9 = 2) R3C9 and (9-6) R2C8 = 6R7C8- (6 = 2) R6C9] => contradiction (two certain 2 in column 9) => - 9R2C8 => stte is a solution that also demonstrates uniqueness.
Ciao a Tutti
Paolo |
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dongrave
Joined: 06 Mar 2014
Posts: 568
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| Posted: Tue Feb 27, 2018 11:49 pm Post subject: |
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| Marty R. wrote: | | Quote: |
Hey! What happened? I remember when Marty would not use a UR to solve a problem on this site! |
Absolutely correct, Don. I've evolved and changed my approach to these puzzles, mostly avoiding the X, XY and XYZ wings. |
Ha! I like the new Marty too! In the old days the Marty I knew would kill a fly with a fly swatter; now he goes right for his AK 47! Old Marty? Or new Marty? I like them both! |
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dongrave
Joined: 06 Mar 2014
Posts: 568
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| Posted: Wed Feb 28, 2018 12:05 am Post subject: |
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| Hey! Wait a minute! I think I found a fly in the ointment with the AK 47 solution. I'm pretty sure that every wing can be expressed as an advanced chain - so even if it's 'possible' to kill a fly with an AK 47, it could have been just as easily killed.. . oh, never mind! I like BOTH Marty's! |
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RobertRattley
Joined: 24 Jun 2007
Posts: 118
Location: Australia
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| Posted: Sun Mar 04, 2018 3:33 am Post subject: |
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| I (also?) will continue to assume all puzzles on this site need at most only X, XY and XYZ wings, unless and until we find that assumption is no longer correct. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Mar 04, 2018 4:27 am Post subject: |
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| RobertRattley wrote: | | I (also?) will continue to assume all puzzles on this site need at most only X, XY and XYZ wings, unless and until we find that assumption is no longer correct. |
That is correct. |
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