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sept 13
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nataraj



Joined: 03 Aug 2007
Posts: 1029
Location: Vienna, Austria

PostPosted: Thu Sep 13, 2007 6:24 am    Post subject: sept 13 Reply with quote

not very hard, when UR looking at it the right way.
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Mindwarp



Joined: 13 Sep 2007
Posts: 25
Location: St. Ives, England

PostPosted: Thu Sep 13, 2007 9:52 am    Post subject: Reply with quote

A fairly easy puzzle. On Draw/Play, first enter all numbers possible without sweep and after that just sweep and eliminate.
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TexCat



Joined: 07 Jul 2006
Posts: 31

PostPosted: Thu Sep 13, 2007 3:07 pm    Post subject: Reply with quote

I got stuck here:
Code:

+------------+----------+---------+
| 23  26  8  | 4  236 5 | 1  9  7 |
| 257 267 9  | 1  26  8 | 25 4  3 |
| 1   4   35 | 27 237 9 | 6  25 8 |
+------------+----------+---------+
| 25  1   7  | 9  8   4 | 25 3  6 |
| 9   25  6  | 3  1   7 | 8  25 4 |
| 8   3   4  | 6  5   2 | 7  1  9 |
+------------+----------+---------+
| 37  79  2  | 5  49  6 | 34 8  1 |
| 6   59  35 | 8  49  1 | 34 7  2 |
| 4   8   1  | 27 27  3 | 9  6  5 |
+------------+----------+---------+

Play this puzzle online at the Daily Sudoku site

What am I missing?
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Thu Sep 13, 2007 3:29 pm    Post subject: Reply with quote

The UR on 27 putting 3 at R3C5, presumably. Since we normally don't seem to have to rely on UR's I'm curious if anyone spotted an XY wing or such.

Peter
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duffy



Joined: 13 Sep 2007
Posts: 26
Location: Toronto Canada

PostPosted: Thu Sep 13, 2007 3:44 pm    Post subject: Reply with quote

Since I learned about UR's (thanks, Keith!) a couple of months ago, I find them interesting and useful. After the previous one for 27's in boxes 2 and 8, there is immediately another one in boxes 1 and 2 on 26's. And for the record, I did not see any wings except for an earlier x-wing on 5's in rows 2 and 4.
I am glad to be back here, after having to re-register since the server problems a few months ago.
Very Happy
Don D.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Thu Sep 13, 2007 6:03 pm    Post subject: Reply with quote

Quote:
What am I missing?


Texcat: From your grid there's a UR that leaves a 7 in R2C1. Though when I did it there was another 257 in R4C1 which, according to Keith's UR post made the UR a Type 2.
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lkmckin



Joined: 25 May 2007
Posts: 9

PostPosted: Thu Sep 13, 2007 6:06 pm    Post subject: Reply with quote

You can use a finned fish on [2] in cols 1 and 7 to eliminate [2] from r2c2.

You can use an XY wing to eliminate [5] from r2c1.

Now, r2c7 is forced to [5] and the rest comes easily after that.

I hate URs because they assume something additional about the puzzle (that it has a unique solution).
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nataraj



Joined: 03 Aug 2007
Posts: 1029
Location: Vienna, Austria

PostPosted: Thu Sep 13, 2007 6:09 pm    Post subject: Reply with quote

sure thing, peter.

from this position
Code:

+--------------------------+--------------------------+--------------------------+
| 23      26      8        | 4       236     5        | 1       9       7        |
| 257     25679   579      | 1       267     8        | 25      4       3        |
| 1       4       357      | 27      237     9        | 6       25      8        |
+--------------------------+--------------------------+--------------------------+
| 257     1       57       | 9       8       4        | 25      3       6        |
| 9       25      6        | 3       1       7        | 8       25      4        |
| 8       3       4        | 6       5       2        | 7       1       9        |
+--------------------------+--------------------------+--------------------------+
| 37      79      2        | 5       49      6        | 34      8       1        |
| 6       59      359      | 8       49      1        | 34      7       2        |
| 4       8       1        | 27      27      3        | 9       6       5        |
+--------------------------+--------------------------+--------------------------+

an xwing in 5 cols 1 and 7,
later on an xy-wing pivot r1c1 (23) with 35-23-25 getting rid of 5 in r2c1 which opens the puzzle.

might have missed an intermediate step or two but those are the highlights I remember
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Marty R.



Joined: 12 Feb 2006
Posts: 5175
Location: Rochester, NY, USA

PostPosted: Thu Sep 13, 2007 6:15 pm    Post subject: Reply with quote

TexCat wrote:
I got stuck here:
Code:

+------------+----------+---------+
| 23  26  8  | 4  236 5 | 1  9  7 |
| 257 267 9  | 1  26  8 | 25 4  3 |
| 1   4   35 | 27 237 9 | 6  25 8 |
+------------+----------+---------+
| 25  1   7  | 9  8   4 | 25 3  6 |
| 9   25  6  | 3  1   7 | 8  25 4 |
| 8   3   4  | 6  5   2 | 7  1  9 |
+------------+----------+---------+
| 37  79  2  | 5  49  6 | 34 8  1 |
| 6   59  35 | 8  49  1 | 34 7  2 |
| 4   8   1  | 27 27  3 | 9  6  5 |
+------------+----------+---------+

Play this puzzle online at the Daily Sudoku site

What am I missing?


There is a Type 6 rectangle in boxes 1 and 2, with the 26 pairs on the diagonal. The four corners are an X-Wing on 6, so the two bivalue cells must be 6 to preclude the deadly pattern. Then remote pairs on 25 take out the 2 from r2c2, leaving it solved with a 7. I don't know offhand if that finishes the puzzle.
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Thu Sep 13, 2007 6:26 pm    Post subject: Reply with quote

nataraj wrote:
an xwing in 5 cols 1 and 7,

Thanks - I seem not very good at X-wings, or, at least, I think I tend to forget to look for them explicitly and to concentrate on XY and XYZ wings.
Peter
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Thu Sep 13, 2007 7:34 pm    Post subject: Reply with quote

I'm going bonkers with this one. According to Texcats grid (and my solution) there is a UR for 257 on R2C17 and R4C17. That should make R2C1 a 7 and eliminate the 7 from R7C1 - but it doesn't - R7C1 is the 7.

Pls help!!
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Marty R.



Joined: 12 Feb 2006
Posts: 5175
Location: Rochester, NY, USA

PostPosted: Thu Sep 13, 2007 7:49 pm    Post subject: Reply with quote

cgordon wrote:
I'm going bonkers with this one. According to Texcats grid (and my solution) there is a UR for 257 on R2C17 and R4C17. That should make R2C1 a 7 and eliminate the 7 from R7C1 - but it doesn't - R7C1 is the 7.

Pls help!!


Craig, the problem is that it is not a rectangle. All the rectangle theories are based on the fact of the rectangle being in just two boxes; the 257 occupies four boxes. With four boxes, there is no "deadly pattern."
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Thu Sep 13, 2007 8:16 pm    Post subject: Reply with quote

Marty.

I didn't know that!! A week ago I thought I was an expert on URs. I was gonna move on to Medusa Wraps. Then on Monday I found out you can't use 3 triples and a quad in a UR - and now the corners have to be in 2 boxes. I should stick to naked-singles.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Thu Sep 13, 2007 9:34 pm    Post subject: Reply with quote

I'd clear that with the significant other first.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Thu Sep 13, 2007 9:56 pm    Post subject: Reply with quote

When I got here (a spot similar to Texcat's and nataraj's position) I saw but decided to ignore the <27> UR in hopes of finding something else, so I went hunting for wings. I missed the (25)(23)(35) with pivot in r1c1 but noticed there was a (23)(35)(25) with pivot in r3c3. Unfortunately, no exclusions were directly possible with it. But applying W-wing with coloring logic (I hope) to the XY-wing, the strong links on <2> show that <2> can be excluded from r1c2.

Code:

 *--------------------------------------------------*
 | 23B  26   8    | 4    236  5    | 1    9    7    |
 | 257  67   9    | 1    26   8    | 25   4    3    |
 | 1    4    35   | 27   237  9    | 6    25A  8    |
 |----------------+----------------+----------------|
 | 25   1    7    | 9    8    4    | 25   3    6    |
 | 9    25A  6    | 3    1    7    | 8    25a  4    |
 | 8    3    4    | 6    5    2    | 7    1    9    |
 |----------------+----------------+----------------|
 | 37   79   2    | 5    49   6    | 34   8    1    |
 | 6    59   35   | 8    49   1    | 34   7    2    |
 | 4    8    1    | 27   27   3    | 9    6    5    |
 *--------------------------------------------------*


One of the cells marked A or B must be 2, because of the XY-wing. Any cell that sees both can be excluded.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Thu Sep 13, 2007 10:49 pm    Post subject: Reply with quote

Tracy,

Your coloring based on the XY Wing is more interesting than you realize.
Code:
*--------------------------------------------------*
|#2R3  26   8    | 4    236  5    | 1    9    7    |
| 257  67   9    | 1    26   8    | 2r5  4    3    |
| 1    4    35   | 27   237  9    | 6    2G5  8    |
|----------------+----------------+----------------|
|#2r5  1    7    | 9    8    4    | 2g5  3    6    |
| 9    2g5  6    | 3    1    7    | 8    2r5  4    |
| 8    3    4    | 6    5    2    | 7    1    9    |
|----------------+----------------+----------------|
| 37   79   2    | 5    49   6    | 34   8    1    |
| 6    59   35   | 8    49   1    | 34   7    2    |
| 4    8    1    | 27   27   3    | 9    6    5    |
*--------------------------------------------------*

The <2>s on the ends of the XY Wing are a conjugate pair (strong link). I've used R and G to mark them, then colored the other conjugates with r and g. Not only is the <2> at R1C2 eliminated by the rg "trap," but there is a color "wrap" caused by having two "reds" in C1, marked #.

So, all of the "red" <2>s can be removed and all the "green" <2>s placed.

(Note: There is no W-Wing type of coloring logic, as discussed recently on another thread, involved here.)
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keith



Joined: 19 Sep 2005
Posts: 3182
Location: near Detroit, Michigan, USA

PostPosted: Thu Sep 13, 2007 10:52 pm    Post subject: Reply with quote

The UR solves it.

Or, there is an XY-wing followed by an X-wing and then a remote pair.

Keith
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Thu Sep 13, 2007 10:54 pm    Post subject: Reply with quote

I'm into ERs (an advanced technique). There's one on 5's from C7 that says R4C3 cannot be a 5. This exposes the UR already alluded to.
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Mogulmeister



Joined: 03 May 2007
Posts: 695

PostPosted: Fri Sep 14, 2007 7:59 am    Post subject: Reply with quote

Empty rectangles (ER) is a technique that (in my opinion) helps out at the early phase of a puzzle and is a nice visual tool. Havard put it forward

http://www.sudoku.com/boards/viewtopic.php?t=3251&start=0

and on his own board.

I find these days that I don't encounter them nearly as much and can only conclude that it is because I am making those eliminations with other strong-link based techniques.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sat Sep 15, 2007 1:54 pm    Post subject: Reply with quote

Asellus wrote:
The <2>s on the ends of the XY Wing are a conjugate pair (strong link).


Are you saying that in all cases the end cells of an XY-wing are conjugate pairs?

Or that in this case they just happen to be the end cells of an XY-wing and just happen to be conjugate?

Cuz, I'm having a hard time seeing either one, but it wouldn't be the first time I missed something like that. I can't think of anything inherent in the XY-wing that precludes them both being <2> and I can't find a simple coloring chain that strongly links them. The cells are linked only in that we know from the XY-wing that at least one of them must be <2>.
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