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Nov 24 VH

 
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Sat Nov 24, 2007 5:52 am    Post subject: Nov 24 VH Reply with quote
sadly, no finned x-wings.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Nov 24, 2007 6:24 am    Post subject: Re: Nov 24 VH Reply with quote
storm_norm wrote:
sadly, no finned x-wings.


That doesn't particularly sadden me, as I hate looking for them. Very Happy

A UR, XY-Wing, W-Wing and another UR did it for me. Both URs were of the Type 1 variety.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Sat Nov 24, 2007 6:28 am    Post subject: Reply with quote
Marty,

did you find that after basics the grid looks like a BUG+2?
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Nov 24, 2007 8:34 am    Post subject: Reply with quote
The basics get you to here:
Code:
+-------------+-------------+-------------+
| 2   7   19  | 45  8   6   | 59  14  3   |
| 15  459 8   | 3   7   2   | 59  14  6   |
| 3   45  6   | 45  9   1   | 7   8   2   |
+-------------+-------------+-------------+
| 7   1   5   | 2   4   3   | 8   6   9   |
| 9   6   2   | 18  15  578 | 4   3   57  |
| 8   3   4   | 9   6   57  | 1   2   57  |
+-------------+-------------+-------------+
| 4   8   7   | 6   2   9   | 3   5   1   |
| 15  2   3   | 7   15  4   | 6   9   8   |
| 6   59  19  | 18  3   58  | 2   7   4   |
+-------------+-------------+-------------+

and the very obvious UR solves R5C6 is <8> and the entire puzzle.

If you don't use the UR, there are a couple of XY-wings to choose from.

And, yes: This is a BUG+2. One of the tri-value cells must be <5>. I don't immediately see how this helps to solve the puzzle.

Keith
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium
PostPosted: Sat Nov 24, 2007 9:42 am    Post subject: Reply with quote
The [45-459-59] XYZ-wing, eliminating <5> in R2C1 is also an alternative

way to solve the puzzle.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Sat Nov 24, 2007 1:28 pm    Post subject: Reply with quote
slept in today.
already time for lunch.

finally...
great, a "very hard"
basics solve the puzzle?
no, not quite.
there's an obvious UR.

Solves the puzzle.
was about to post.
see keith's post.
my position exactly.

well, well...

edit: and, yes. Not to sound xx or anything, but I do prefer the

very-er hards

Did a "hard" today in the local paper took me longer than this one. Hm
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada
PostPosted: Sat Nov 24, 2007 1:52 pm    Post subject: Reply with quote
I didn't get as far as Keith with the basics so I had an extra <8> in R5C9. But this made it a Type 2 UR (I think) which knocked out the <8> in R5C4. That's all it needed.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Nov 24, 2007 4:23 pm    Post subject: Reply with quote
storm_norm wrote:
Marty,

did you find that after basics the grid looks like a BUG+2?


Norm, I really don't remember, but I suspect the answer is "no", because if it did I probably would've solved it with fewer moves than I did.
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Nov 24, 2007 7:15 pm    Post subject: Nov 24 VH Reply with quote
From Keith's grid there is a simple xy-wing pivoted at R1C3 which finishes the puzzle. But you had to be alert to reach Keith's grid.

Earl
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Nov 24, 2007 8:08 pm    Post subject: Reply with quote
Quote:
From Keith's grid there is a simple xy-wing pivoted at R1C3 which finishes the puzzle.


An alternative way to make the same move is to use the W-Wing on 59 which is connected by the 9s in column 3. The pincer 5s do not eliminate anything though. But if you color the 5s from r2c9-->r1c8-->r1c2, you then end up with the same pincers as the XY-Wing.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Nov 24, 2007 9:01 pm    Post subject: Re: Nov 24 VH Reply with quote
Earl wrote:
But you had to be alert to reach Keith's grid.


Actually, not really. This puzzle is a great example of why you should not fill in all the pencil marks. I work without an PM's as long as I can, then I put PM's only in cells that have two candidates.

Eventually you may have to fill in all the PM's, but in the early stages of a puzzle I try to see the patterns in the solved cells, not in the PM's.

If you'd like to practice recognizing pairs and triples by looking at the solved cells, try the the hardest "fiendish" puzzles at Fiendish Sudoku. Twisted Evil
http://www.fiendishsudoku.com/sudoku.html

These don't require much more than the occasional X-wing, but if you start by filling in all the PM's, they'll drive you crazy.


Keith
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales
PostPosted: Sun Nov 25, 2007 7:43 am    Post subject: Reply with quote
Just the simple xy-wing was all I saw, followed by the complete collapse of the puzzle; it was easy to spot because there weren't a lot of unsolved cells left at that stage.

Not a very hard VH, I thought, but a very satisfying one. Smile

John
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re'born



Joined: 28 Oct 2007
Posts: 80
PostPosted: Sun Nov 25, 2007 1:11 pm    Post subject: Reply with quote
keith wrote:
The basics get you to here:
Code:
+-------------+-------------+-------------+
| 2   7   19  | 45  8   6   | 59  14  3   |
| 15  459 8   | 3   7   2   | 59  14  6   |
| 3   45  6   | 45  9   1   | 7   8   2   |
+-------------+-------------+-------------+
| 7   1   5   | 2   4   3   | 8   6   9   |
| 9   6   2   | 18  15  578 | 4   3   57  |
| 8   3   4   | 9   6   57  | 1   2   57  |
+-------------+-------------+-------------+
| 4   8   7   | 6   2   9   | 3   5   1   |
| 15  2   3   | 7   15  4   | 6   9   8   |
| 6   59  19  | 18  3   58  | 2   7   4   |
+-------------+-------------+-------------+

And, yes: This is a BUG+2. One of the tri-value cells must be <5>. I don't immediately see how this helps to solve the puzzle.

If r3c2=5, then r9c2<>5 and hence r9c6=5. This kills both BUG candidates and so r3c2<>5, solving the puzzle.
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DennyOR



Joined: 12 Sep 2007
Posts: 33
Location: Portland, Oregon
PostPosted: Tue Nov 27, 2007 8:42 am    Post subject: Reply with quote
From Keith's position a 15-54-45-54-41 xy chain solved it for me.
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