The New Sudoku Players' Forum

[StrmCkr]

there is competitions for sudoku solving.....

[aran]

Technically UR78 doesn't really exist (2r13c7 being forced).
7r8c7=8r2c7 holds independently in any case.

I think its valid...
but this forces me to find a better example.
unless you find one before me, aran.

Here's one contender Storm Norm :
UR39 avoidance r78c29 =>5r7c2=4r8c9
then : 5r7c2=4r8c9-(4=7)r9c8-(7=3)r8c7-(3=9)r8c2 : =><9>r7c2

aran, that's another Type 6 UR as mentioned on page 1, so you can add <9>r8c9.

FWIW, IMHO and no criticism
All that UR typology is a bit over the top...
Those "types" could merely have been used as illustrations of the uniqueness force at work.
Once the solver has grasped the concept, he will make those deductions in less time that it takes to wonder if he has a type III situation...
In other words, if the pattern takes longer than doing the logic, forget the pattern.
What's more, uniqueness logic is entertaining, so why divert the solver towards "format"

[Luke]

In other words, if the pattern takes longer than doing the logic, forget the pattern.
What's more, uniqueness logic is entertaining, so why divert the solver towards "format";)

I was just pointing out the other elimination in your UR .

When I recognize a particular UR patern, I never think, "Oh, that's a Type this or that." There are situations where one can instantly recognize the eliminations, so doing the pattern would not take longer than doing the logic.

On the other hand, I understand the point your making. A UR exerts influence beyond the immediate pattern, and if one is too focused on the four walls he'll lose the solving (and entertainment) value of the UR. I'm definitely guilty of doing that, and it's the main lesson that I'm taking away with me from SAM #1.

It’s what eleven used to backdoor the puzzle without the interaction of any other techniques. It’s what StrmCkr applied when he was the first to crack the puzzle with his MUG, or udosuk with a rewriting of the same move. There’s your use of the UR in chain 1 (did I mention it was a Type 1? ) or storm norm and ronk with chain observations, or DonM with his vertical from page one, and so on. All suggest the same lesson: learning one’s URs is one thing, but getting the most from them is another.

[DonM]

IMO, there is a very useful place for assigning type categories to structures such as URs. They allow for basic pattern solving serving the same purpose as other patterns whereby simply seeing the pattern without having to analyze the logic behind it justifies the elimination. Not only that, but it makes it easier to transmit from one person to another what was found ie. 'there is a Type 6 UR there' as opposed to describing the various links in the structure. The organizing of certain basic patterns into these Types is also beneficial in the authoring of tutorials and books.

The upshot is that there are a lot of people who are not blessed with the type of natural skills that allow one to see the underlying relationships as quickly or more quickly than recognizing a given pattern, skills that a number of very talented people on this forum have. The use of organized patterns gives the boolean-logic-limited masses a place to start.

What I see as Aran's main point though is important: to really get the benefit & power of URs is to not rely on Types, but to understand the underlying logic. Just my view.

[storm_norm]

aran,
how about this one?

Code: Select all

.---------------------.---------------------.---------------------.
| 2     *34589  158   | 18     57     6     |*35789  145   *489   |
|*145    6      158   | 3      57     9     | 578    1245   248   |
|U1359  U3589   7     | 4      2      18    |*3589   6     *89    |
:---------------------+---------------------+---------------------:
| 8      1      3     | 9      4      5     | 2      7      6     |
|U59    U59     2     | 6      1      7     | 4      8      3     |
| 6      7      4     | 2      8      3     | 1      9      5     |
:---------------------+---------------------+---------------------:
| 1345   3458   158   | 7      6      48    | 589    245    2489  |
| 7      458    9     | 58     3      2     | 6      45     1     |
|*45     2      6     | 158    9      148   |-58     3      7     |
'---------------------'---------------------'---------------------'

notice the UR cells marked on {5,9}. the UR says that in order to avoid the deadly pattern, both the 5 in r3c7 and the 9's in r3c79 can't all be false.
in other words, UR59[(5)r3c7 = (9)r3c79]... which can be extended to eliminate the 5 in r9c7...
UR59[(5)r3c7 = (9)r3c79] - (9)r1c79 = (9-4)r1c2 = (4)r2c1 - (4=5)r9c1; r9c7 <> 5

[DonM]

If there's any dirty laundry left in this puzzle, storm_norm is going to find it.

[aran]

aran,
how about this one?

Code: Select all

.---------------------.---------------------.---------------------.
| 2     *34589  158   | 18     57     6     |*35789  145   *489   |
|*145    6      158   | 3      57     9     | 578    1245   248   |
|U1359  U3589   7     | 4      2      18    |*3589   6     *89    |
:---------------------+---------------------+---------------------:
| 8      1      3     | 9      4      5     | 2      7      6     |
|U59    U59     2     | 6      1      7     | 4      8      3     |
| 6      7      4     | 2      8      3     | 1      9      5     |
:---------------------+---------------------+---------------------:
| 1345   3458   158   | 7      6      48    | 589    245    2489  |
| 7      458    9     | 58     3      2     | 6      45     1     |
|*45     2      6     | 158    9      148   |-58     3      7     |
'---------------------'---------------------'---------------------'

notice the UR cells marked on {5,9}. the UR says that in order to avoid the deadly pattern, both the 5 in r3c7 and the 9's in r3c79 can't all be false.
in other words, UR59[(5)r3c7 = (9)r3c79]... which can be extended to eliminate the 5 in r9c7...
UR59[(5)r3c7 = (9)r3c79] - (9)r1c79 = (9-4)r1c2 = (4)r2c1 - (4=5)r9c1; r9c7 <> 5

Storm Norm
That's a beauty

PS humdrumly note that UR avoidance on 57r12c57, given 7 forced over r12c7 => <5>r12c7

[storm_norm]

PS humdrumly note that UR avoidance on 57r12c57, given 7 forced over r12c7 => <5>r12c7

yep, so noted.

[999_Springs]

Totally digressing for a moment. Has anyone noticed how bizarre the situation is at the moment when it comes to a person trying to learn how to solve Sudoku using basic & advanced methods? I went into Borders (a book store chain for those not in the U.S.) the other day and just for the heckuvit checked out the Sudoku section. There were easily over 100 Sudoku books with all sorts of names. While right next to them were books on Chess, Bridge with indepth descriptions on how to play them, not one of the Sudoku books had anything more than 1-3 pages on very rudimentary instructions on how to solve a sudoku puzzle (eg. pretty much limited to cross-hatching, perhaps basic naked pairs and the like.) and most of them had nothing. If you were lucky you might come across Paul Stephen's Mastering Sudoku which is probably the best book available for basic methods now that Andrew Stuart's 'Logic of Sudoku' is sadly unavailable now. Otherwise there's virtually nothing that would teach someone how to logically solve a puzzle. Which means that any person trying to get to the level of those on this forum have got a lot of hard-core sleuthing to do.

Hmmm... maybe it could also be because Su-Doku is only a few years old (how many exactly?) and chess and the like are many hundreds of years old. So as a result of this, there are more competitions relating to chess etc..

With regard to Su-Doku related competitions, I don't really see how they can work unless you're timed for solving a puzzle, and, uh, timed solving seems to have left the world of Su-Doku in about 2006.

[storm_norm]

and, uh, timed solving seems to have left the world of Su-Doku in about 2006

I have read many sources that claim timed chess games dilute the level of play.

[999_Springs]

I have read many sources that claim timed chess games dilute the level of play.

That is going to be one of my favourite quotes of all time. Whenever I play chess everyone complains about how slow I move because I'm the sort of person who tries to calculate everything before touching the board. I have played chess with a clock for three years and in that time I have won on time just once and lost on time about... once every three or four weeks. Could you point me towards one of the sources?

But still, I think that chess clocks are certainly here to stay, no matter how strong the evidence may be that they are positively evil. (Sigh.) This is very much unlike Su-Doku, where timed competitions just seem not to exist anymore. (Well at least I can't find any.) Maybe it is because if you have a puzzle rated above SE=5 or 6, it is actually faster to abandon logical techniques altogether and guess one (or both simultaneously) candidate in a bivalue/bilocation. This sort of ruins the point of solving puzzles by logic. But then you're going to have to find another way to invent a competition, which is difficult, as there isn't much left to compete for.

[DonM]

For me at least, reasons based on the fact that Sudoku is relatively new & is not usually practised on a competitive basis may explain why there are not many Sudoku books on logic-based techniques, but doesn't explain why there is only one (the aforementioned Mastering Sudoku), The Logic of Sudoku no longer being available.

[storm_norm]

I have read many sources that claim timed chess games dilute the level of play.

That is going to be one of my favourite quotes of all time. Whenever I play chess everyone complains about how slow I move because I'm the sort of person who tries to calculate everything before touching the board. I have played chess with a clock for three years and in that time I have won on time just once and lost on time about... once every three or four weeks. Could you point me towards one of the sources?

But still, I think that chess clocks are certainly here to stay, no matter how strong the evidence may be that they are positively evil. (Sigh.) This is very much unlike Su-Doku, where timed competitions just seem not to exist anymore. (Well at least I can't find any.) Maybe it is because if you have a puzzle rated above SE=5 or 6, it is actually faster to abandon logical techniques altogether and guess one (or both simultaneously) candidate in a bivalue/bilocation. This sort of ruins the point of solving puzzles by logic. But then you're going to have to find another way to invent a competition, which is difficult, as there isn't much left to compete for.

use of the word "dilute" was probably not good.
"robotic" is a better word. timed play encourages memorizing openings... gambits... endings, what have you.
the game then takes on a programmed feel.
so instead of chess being a game of skill on the board, it now has become a game of skill and time management. which for those who play chess online know all too well.
memorizing moves for a particular situation just so you can beat the clock??
does that make you a good chess player?
it does now.
http://www.chesscafe.com/text/time.txt
http://query.nytimes.com/gst/fullpage.html?res=9B0DE2DD1431F933A15753C1A961948260

[Luke]

I think there is an element of winning or losing in any puzzle solving. Either one wins or the puzzle does. RW once said if the puzzle is a devil, what could be more fun than beating the devil? There is personal satisfaction in beating the puzzle, and it is a strong motivator. Whole genres of video games are based on figuring out a succession of puzzles, and it can be very satisfying/addicting to succeed (like we don't know!) It's a form of self-affirmation. No one wants their butt kicked by a sports or chess opponent, but you don't want to be schooled by the New York Times crossword, either.

Maybe most folks are happy with the grade of puzzle they find in the newspaper or bookstore. They win, most days, and that feels good. What good is a text full of esoterica to them? I found this out for myself:

Last August my sister was visiting from out of state. In the evening, she reaches into her bag and pulls out a supermarket Sudoku collection. I told her that I didn't know she did "those things," and she says something like, "Yes, almost every day. They relax me. I can do all of them except for the hard ones in the back." I say, well let's look at one of the "hard ones in the back." You can only imagine the misinformation I proceeded to feed her.

By the end of the visit she had solved all the "hard" ones in her book and she left all fired up. A while back, I asked how her solving was going, and I was surprised to hear her say that it wasn't much fun for her any more! Why? With a few tricks up her sleeve, her pulp Sudoku books were too easy and the "internet" ones were too hard. She had pretty much stopped doing them, and joked that I had "ruined her fun!" I offered to help her find ones she liked, and she said, "That's OK, I'd rather do my weaving now. At the end of the day at least I have something to show for all my work!" Ouch....

Too bad. I had an almost jellyfish in a nice loop I wanted to sell her....

[DonM]

Too bad. I had an almost jellyfish in a nice loop I wanted to sell her....

Luke, has the recession reduced you to trying to make money off my almost jellyfish?