Diffcult Puzzle

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Postby ronk » Thu Nov 27, 2008 2:33 am

hobiwan wrote:In short: The notation follows the Nice loop propagation rules (see http://www.paulspages.co.uk/sudokuxp/howtosolve/niceloops.htm for a tutorial).

Use a double dose of salt with a tutorial that makes the statement ...

One danger with Nice Loop notation is that you can't always tell whether it's correct or not, because the notation alone doesn't tell you whether squares with two weak links are bivalue. -- Paul Stephens

Has Paul Stephens ever posted here?
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Postby DonM » Thu Nov 27, 2008 5:56 am

ronk wrote:
hobiwan wrote:In short: The notation follows the Nice loop propagation rules (see http://www.paulspages.co.uk/sudokuxp/howtosolve/niceloops.htm for a tutorial).

Use a double dose of salt with a tutorial that makes the statement ...

One danger with Nice Loop notation is that you can't always tell whether it's correct or not, because the notation alone doesn't tell you whether squares with two weak links are bivalue. -- Paul Stephens


Au contraire, just for the benefit of anyone who might be referred to it, it's the only real nice loop tutorial available and IMO it's an excellent one.

So, the notation makes it particularly clear that 'squares with two weak links are bivalue'?
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Postby ronk » Thu Nov 27, 2008 6:03 am

DonM wrote:So, the notation makes it particularly clear that 'squares with two weak links are bivalue'?

Au contraire, Paul Stephens used the term correct rather than clear. There is a difference.
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Postby DonM » Thu Nov 27, 2008 6:22 am

ronk wrote:
DonM wrote:So, the notation makes it particularly clear that 'squares with two weak links are bivalue'?

Au contraire, Paul Stephens used the term correct rather than clear. There is a difference.


Not enough to suggest that the accuracy of an excellent tutorial, which took someone a lot of work, is in question.
Last edited by DonM on Thu Nov 27, 2008 2:24 am, edited 1 time in total.
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Postby DonM » Thu Nov 27, 2008 6:23 am

daj95376 wrote:DonM: I agree with hobiwan for the AIC in Eureka notation.


As do I.:)
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Postby ronk » Thu Nov 27, 2008 6:46 am

DonM wrote:
ronk wrote:
DonM wrote:So, the notation makes it particularly clear that 'squares with two weak links are bivalue'?

Au contraire, Paul Stephens used the term correct rather than clear. There is a difference.

Not enough to suggest that the accuracy of an excellent tutorial, which took someone a lot of work, is in question.

Considering that there's isn't that much to understand about nice loop notation, the quoted statement ...

One danger with Nice Loop notation is that you can't always tell whether it's correct or not, because the notation alone doesn't tell you whether squares with two weak links are bivalue. -- Paul Stephens

... indicates less than a full understanding of the notation. Indeed, I think it's a serious error.
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Postby daj95376 » Thu Nov 27, 2008 7:43 am

Ahhhh, are we beating the obvious to death here?

Does anyone have an example of a cell with two weak links that isn't a bivalue cell? (This does not include loops!)

If not, then this is where I think Paul Stevens dropped the ball on this topic. As for the rest of his presentation, it looks like a lot of hard effort went into it, and I commend him for it!
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Postby aran » Thu Nov 27, 2008 8:17 am

daj95376
Does anyone have an example of a cell with two weak links that isn't a bivalue cell?


r9c1=478...once you're into abbreviation, then why not abbreviate this :

4r1c1-(4=78)r9c1-ALS(4789)r9c145=789r9c145-(789=5)r9c9

to 4r1c1-4r9c1-ALS(4789)r9c145-(789=5)r9c9

Same idea : abbreviate the obvious...with its advantages and disadvantages.
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Postby ronk » Thu Nov 27, 2008 8:47 am

aran wrote:why not abbreviate this :

4r1c1-(4=78)r9c1-ALS(4789)r9c145=789r9c145-(789=5)r9c9

to 4r1c1-4r9c1-ALS(4789)r9c145-(789=5)r9c9

Debating NL notation using AIC notation makes no sense to me.
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Postby aran » Thu Nov 27, 2008 2:41 pm

ronk wrote:
aran wrote:why not abbreviate this :

4r1c1-(4=78)r9c1-ALS(4789)r9c145=789r9c145-(789=5)r9c9

to 4r1c1-4r9c1-ALS(4789)r9c145-(789=5)r9c9

Debating NL notation using AIC notation makes no sense to me.


If you speak English and French reasonably well, but Swahili is your mother tongure...then that would not be a parallel.
Some speak NL, some speak Eureka, but we all speak common sense.
All sudoku logic is simple, even simplistic, so simple that we'd all like to skip certain boring steps.
NL does that to a limited extent by skipping logic within bivalues (and why not).
AIC or Eureka, or whatever it is called, seems to prefer each laboured step to be stated (and why not)..
Neither system can easily handle something as straightforward as an xyt-chain ie chain with memory.
I don't know whether Denis Berthier created this term but he is certainly its foremost exponent (so far as I know) and he makes this point somewhere (that xyt has no easy outlet in NL or AIC)
This IMHO is an indictment of NL/AIC.
But back to the point "debating NL using AIC makes no sense".
Response : of course it makes sense.
Each in an impoverished attempt to state the obvious ; no solver starts with NL or AIC : he sees an elimination via some logic, then he seeks to express it in NL or AIC.
Said otherwise, he speaks common sense, then he has to fit that into deficient notation.
So since each is deficient, why not compare their demerits ?
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Postby ronk » Thu Nov 27, 2008 3:06 pm

aran wrote:"debating NL using AIC makes no sense".
Response : of course it makes sense.

This is not Eureka!
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Postby aran » Thu Nov 27, 2008 3:28 pm

ronk wrote:
aran wrote:"debating NL using AIC makes no sense".
Response : of course it makes sense.

This is not Eureka!

Just a little too elliptical. Can you elaborate ?
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Postby Jasper32 » Thu Nov 27, 2008 4:01 pm

I want to thank all of you for your input and advise. Yes, I have learned quite a bit and have studied and printed-out the URL’s that were referenced in the various posts. For me, a neophyte at working Sudoku puzzles, it has been very interesting reading your posts as well as informative.

I will stick, for now at least, with the, “5[r5c8]=5[r6c9]-1[r6c9]=1[r8c9]-1[r8c7]=7[r8c7]-7[r2c7]=7[r2c5]-7[r3c6]=8[r3c6]-8[r3c9]=5[r3c9]” type of notation because I understand it. Actually, in comparing it with Hobiwan’s notation, I can now understand what he was doing and see the so-called “short-cut’s”.

I cannot understand why more people don’t avail themselves to posting on this forum. You have been treasure trove of help, for me, in understanding some of the more involved and complicated Sudoku strategies.

Again, many thanks
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