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DB Saturday Puzzle - September 2, 2006
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keith



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

PostPosted: Sat Sep 02, 2006 12:34 pm    Post subject: DB Saturday Puzzle - September 2, 2006 Reply with quote

I have not yet looked at this one ...
Code:
Puzzle: DB090206  ******
+-------+-------+-------+
| 8 1 . | 7 . . | 3 2 . |
| . . 7 | . . 5 | . . 8 |
| . 6 4 | 2 8 . | . . . |
+-------+-------+-------+
| . . . | 6 . . | . . 1 |
| . 8 . | 4 . 2 | . 9 . |
| 7 . . | . . 8 | . . . |
+-------+-------+-------+
| . . . | . 2 4 | 9 3 . |
| 4 . . | 5 . . | 1 . . |
| . 2 9 | . . 7 | . 4 5 |
+-------+-------+-------+


Keith
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Sat Sep 02, 2006 1:33 pm    Post subject: Reply with quote

Hi, Keith!

Just for grins, I ignored the "UR" in r18c56 ... I found an interesting "Nishio" sort of move on the "6"s instead. dcb
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keith



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

PostPosted: Sat Sep 02, 2006 3:24 pm    Post subject: XYZ-wing Reply with quote

Dvaid,

If you do not use the UR, there is an XYZ-wing in the lower left corner that solves it.

Keith
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Marty R.



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

PostPosted: Sat Sep 02, 2006 3:55 pm    Post subject: Reply with quote

I thought this one wasn't up to the usual standards of his six-star ratings, as it was solvable with nothing more than the basic techniques of pairs, triples, etc. and locked candidates.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Sat Sep 02, 2006 11:29 pm    Post subject: Is this the "XYZ Wing"? Reply with quote

Keith wrote:
If you do not use the UR, there is an XYZ-wing in the lower left corner that solves it.

I guess this amounts to the same thing as the XYZ Wing, Keith. The easy moves got me to here.
Code:
  8     1     5     7    469    69    3     2     46+
  2     9     7     3     46+   5     46-   1     8
  3     6     4     2     8     1     57    57    9
  9     45    2     6     57    3    4578  578    1
 156*   8    136+   4    157    2     57    9     37
  7    345    13    9     15    8    245    6     34
 156+   57   168*   18    2     4     9     3     67-
  4     37    38    5     69    69+   1     78    2
  16-   2     9     18    3     7     68+   4     5

Looking for the "spiral pattern" on a single digit, I noticed the "6"s.

r9c7 = 6 ==> r1c9 = 6 ==> r2c5 = 6 ==> r8c6 = 6

Also, r9c7 = 6 ==> r7c9 = 7 ==> r7c2 = 5; r9c7 = 6 ==> r9c1 = 1
(r9c1 = 1 & r7c2 = 5) ==> r7c1 = 6 ==> r5c3 = 6

See the "+" marks in the grid above. This is good enough to let us do some coloring:

r9c7 <> 6 ==> (r2c7 = 6 & r7c9 = 6 & r9c1 = 6)

See the "-" signs above. We can eliminate "6" from r5c1 and r7c3, and that's enough to solve the puzzle. dcb

PS I think the "XYZ Wing" is in r7c1, r7c2, r7c9, and r9c1 -- at least, I can see why r7c3 = 6 is not possible, based on those four cells.
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keith



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

PostPosted: Sun Sep 03, 2006 12:44 am    Post subject: XYZ-wing Reply with quote

The XYZ- wing is on <168> in R7C3. It takes out <1> in R7C1.

Let me try to explain. Both XY-wings and XYZ-wings are naked triples spread over more than one box or line. The XYZ-wing is much weaker, and much less common.

For example:

Here is an XY-wing. It eliminates Z from the cells labeled #. (The common buddies of the "wing" cells, the ones containing <Z>.)
[9/3: Edited to fix an error in the following diagram. Thanks, Tracy!]

Code:
+----------+--------+
| #  #  XY | . XZ . |
| .  .  .  | . .  . |
| YZ .  .  | # #  # |
+----------+--------+


Here is an XYZ-wing. It eliminates Z from the cells labeled #. (The common buddies of all three cells, the ones containing "Z".)

Code:
+----------+--------+
| #  # XYZ | . XZ . |
| .  .  .  | . .  . |
| YZ .  .  | . .  . |
+----------+--------+


Keith


Last edited by keith on Sun Sep 03, 2006 1:59 pm; edited 1 time in total
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TKiel



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

PostPosted: Sun Sep 03, 2006 12:13 pm    Post subject: Reply with quote

Keith,

I know you know this and it was probably just an oversight, but wouldn't an XY-wing also take out the Z candidate in the (#) cell?

Code:

+----------+--------+
| #  #  XY | . XZ . |
| .  .  .  | . .  . |
| YZ .  .  | # # (#)|
+----------+--------+
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Marty R.



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

PostPosted: Sun Sep 03, 2006 3:57 pm    Post subject: Reply with quote

Keith/David,

Obviously you guys enjoy looking around for more advanced techniques to use than are required to simply complete the puzzle. So the question I pose is this: at what point in doing a puzzle do you stop eliminating candidates with basic techniques and start looking for more advanced stuff?
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TKiel



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

PostPosted: Sun Sep 03, 2006 5:24 pm    Post subject: Reply with quote

Marty R. wrote:
...at what point in doing a puzzle do you stop eliminating candidates with basic techniques and start looking for more advanced stuff?


I know you didn't ask me, Marty, (since I said on at least a couple of occassions that I don't do that) but I'll reply anyway. :)

1. When I'm done doing the puzzle the fastest and easiest way I can find AND

2. Somebody mentions that there is a different way to solve the puzzle OR

3. Somebody says that at a certain point a certain technique MUST be used.

That's when it's extremely handy to be able to load the puzzle into one of the many solvers that are available. Depending on the solver, you can save the puzzle, use the hint feature to get the next move, print out a sequence of solving steps, disable some solving techniques or backtrack to the beginning of the puzzle. And justify it to your spouse/boss as a quest to become a more knowledgeable/logical person.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sun Sep 03, 2006 9:16 pm    Post subject: Reply with quote

Tracy, you would convince me to use a program, but Marty ??

Marty,
to your question: it depends on, what candidates i already have filled in. Sometimes i also can see a short chain with few candidates, before i am able to spot an x-wing, xy-wing or coloring. Also xyz-wings are sometimes easy to spot, it is like looking for triples "round the corner".
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Sun Sep 03, 2006 10:37 pm    Post subject: When I get tired ... Reply with quote

Marty R wrote:
... at what point in doing a puzzle do you stop eliminating candidates with basic techniques and start looking for more advanced stuff?

I stick with the basic techniques until I can't find anything else obvious, or until I get tired, whichever comes first. Smile

Actually, it depends a lot on the puzzle. Sometimes a short double-implication chain just seems to jump out at me. When that happens, I use it. In most puzzles, though, I have to look for the useful chains, and that's hard work. So I generally don't look for them until I can't find anything simpler. dcb
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Marty R.



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

PostPosted: Mon Sep 04, 2006 12:29 am    Post subject: Reply with quote

Tracy/Ravel,

I haven't gotten into using the various solvers since I'm not very tech-savvy.

David,

Maybe I misinterpreted something. For me, this puzzle required only very basic techniques, but with all the talk of URs, Nishio, XY, XYZ and chains, I didn't realize that you went with basic as far as you could.
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TKiel



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

PostPosted: Mon Sep 04, 2006 12:46 am    Post subject: Reply with quote

Marty R wrote:
David,

Maybe I misinterpreted something. ...I didn't realize that you went with basic as far as you could.


I know what you mean. I thought he started constructing DIC's from the moment he set eyes on a puzzle. Very Happy
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Mon Sep 04, 2006 3:59 am    Post subject: Working without "UR"s Reply with quote

Marty R wrote:
... this puzzle required only very basic techniques, ...

After making 16 simple moves I hit a spot where there was a "type 1 unique rectangle" in r18c56. I could have assumed that the solution was unique, then put a "4" in r1c5, and gone merrily on my way.

Generally when I see a "UR" I try to work the puzzle without using it. It's just a little quirk of mine, to make some puzzles a bit more interesting. dcb
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Marty R.



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

PostPosted: Mon Sep 04, 2006 8:46 pm    Post subject: Reply with quote

Quote:
After making 16 simple moves I hit a spot where there was a "type 1 unique rectangle" in r18c56. I could have assumed that the solution was unique, then put a "4" in r1c5, and gone merrily on my way.


David,

I've had a private discussion about this puzzle with Keith. I did it a second time and used that UR you speak of. So I may have been in error when I said I solved it with only very basic techniques. I just have no way of knowing exactly how I solved it the first time. Usually I write in the margins the techniques I used and there were no such notations on the first one. I don't know if I used the UR and forgot to note it or solved it without using it.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Mon Sep 04, 2006 9:18 pm    Post subject: No big deal ... Reply with quote

Marty --

The cool thing about the "UR" techniaue -- especially the Type 1 UR -- is that it's so easy to spot and so simple to use that one can easily start thinking of it as a very basic technique. I've even used it that way on some simple puzzles in the newspaper -- not because I couldn't see some other way to go, but because I was in a hurry and the inference "have to put a 2 right here" seemed so simple. Heck -- I've even gotten into the habit of looking, when I spot a pair that lies in one 3x3 box, to see if there might possibly be another pair somewhere that lines up with this one and gives me a "UR." It's a great device for visualizing the structure of a puzzle. dcb


Last edited by David Bryant on Tue Sep 05, 2006 11:42 am; edited 1 time in total
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Marty R.



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

PostPosted: Tue Sep 05, 2006 1:31 am    Post subject: Reply with quote

David, that's true, a Type 1 is easy and could be a basic technique, perhaps even easier than some techniques widely considered to be basic. But I tend to stick with what I learned when I was just starting out, and URs were considered advanced. So when I refer to basic techniques, it's pretty much limited to pairs, triples, etc., and locked candidates.
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AZ Matt



Joined: 03 Nov 2005
Posts: 63
Location: Hiding under my desk in Phoenix AZ USA

PostPosted: Tue Sep 12, 2006 4:49 pm    Post subject: Just chiming in... Reply with quote

My two cents on when you start looking for more complicated solves:

I have done very difficult puzzles that were boring and very easy puzzles that were fascinating. As this forum demonstrates, I think we are all interested in puzzles that have multiple solutions involving varying degrees of difficulty. I define boring as puzzle that plods forward on one path, and fascinating as puzzles that show opportunities for multple paths and new or rare solving techniqes.

It is true, however, that the very best puzzles are the ones that can ONLY be solved by using a new or rare technique, whether they plod to that point or offer multiple ways of getting to that point.

So my answer to the question is, "It depends on the puzzle..."
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keith



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

PostPosted: Tue Sep 12, 2006 5:39 pm    Post subject: Reply with quote

Quote:
we are all interested in puzzles that have multiple solutions

Meaning, I think, puzzles that can be solved in multiple ways.

Keith
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Marty R.



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

PostPosted: Tue Sep 12, 2006 9:40 pm    Post subject: Reply with quote

Quote:
It is true, however, that the very best puzzles are the ones that can ONLY be solved by using a new or rare technique, whether they plod to that point or offer multiple ways of getting to that point.


Matt, do you know of a puzzle source that consistently offers puzzles that meet that criterion?

One of the things that I think I've learned since joining the forum is that even puzzles that are considered by most people to be of high quality have multiple techniques that will solve it.

On a number of occasions I've seen people say that, for example, such-and-such puzzle needs an XY-Wing, followed by comments from others who described how they solved it without the "necessary" XY-Wing.
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