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# Feedback and Questions

I've received a lot of interesting comments and questions from Sudoku fans over the last few years and this page is where I try to answer them. I'm also directing Str8ts feedback here. Please feel free to drop me a note on the side of the page. Or you can email me directly at .

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Any Sudoku you want to publish here for easy loading into the solver - 81 characters, use '.' or '0' for unknowns.

 public - comment/question will be added to feedback column private - email comment/question directly to Andrew Stuart, don't display here

Comment, question or feedback:

letters you see:

Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

## ... by: Carol, Victoria BC, Canada

Happy Birthday, Andrew!! And thank you for all you offer on this wonderful site. CM

Andrew Stuart writes:
Thanks Carol !

## ... by: Robert Messer, BC, Canada

I am trying to understand the 3D Medusa rules. Things were going fine until I attempted the attached puzzle. Apparently, there is something I don't understand as there seems to be a contradiction to the basic colouring logic. If I have typed the puzzle in correctly, there should be bi-value cells at J7 (69), another at E7 (36) and E3 (68). If I link these 3 cells the colours of 6's at J7 and E3 should be the same. A peek at the answer key says the 6 at J7 is a solution but the 6 at E3 is not. What am I not understanding about Medusa logic?

Andrew Stuart writes:
You are trying to connect cells on a value X where there are more than two X in the row or column. Say J7 was 6, yes you can turn of 6 in E7 - cos you have to turn off ALL 6s in the columns. But -6 in E7 does not imply +6 in E3 - because there are other 6s in the row.

The only way you can skip over clusters of X using bi-value cells is if ther bi-value cells contain the same numbers, eg Remote Pairs. Check the second half of X Cycles

## ... by: John Gallagher, Seal Beach, CA

Andrew, When I have to use "Bowman's Bingo" to solve a puzzle, It feels like I am simply guessing as opposed to actually solving.
What are your thoughts on this?

Thanks
John Gallagher

Andrew Stuart writes:
I agree, it is more or less equivalent to guessing. Back in the day, there were quite a few entertaining ideas about how to guess "methodically" and this was one of them. I happened to implement it as it was an algorithm I could grasp (more or less) and could have led somewhere. I do have it under the "trial and error" label on the site.

Fortunately you can keep strategies turned off now (with cookies enabled)

## ... by: Peter, Indonesia

I love your solver. I've used it for several years primarily to improve my skill at identifying chains and loops. Thank you for the effort you make in providing such an excellent tool. I solved the above puzze using the bivalue universal grave (BUG) rule which I'm sure you've seen before. Out of curiosity, I entered in into your solver to see what happens. At the point where the BUG appears, the solver identifies two XY chains that solve the puzzle. So it is only one extra step. As I'm sure you know, the BUG rule always solves the puzzle in one step when it applies. However, I would say it appears in fewer than 1% of all puzzles. Despite its rarity, have you considered adding it to the solver? The logical place for it would be as the final tough strategy following XYZ wing.

Andrew Stuart writes:
I currently don’t have BUG, but I'm interested in adding it. I did have a special instance of BUG way back at the start but I knew it was not a generalised enough and what with one thing and another, I lost the original discussion of it. In 2010 I removed it from the solver as it was quite useless. Still have the docs page though. If you can describe the principle to me I can have another go, been annoying me this for some time

## ... by: stripey, England

I love this site!
Is there any chance that the book will be published again, even as a paid download? It's very tantalising knowing that it exists but that I can't get hold of it!
Thanks.

Andrew Stuart writes:
Yes I do hope to release a eBook version. I could export the site documentation quite easily but I think a purchaser would expect more than that. I do have several discussive chapters ready which will form the start of the book, but overall I want to include new examples. The the problem becomes one of proof checking, which is a night mare considering how problematic the paper book was. At least I could update a e-version. So it’s a bigger job that it seems but I do want to do it.

## ... by: jerry, georgia, usa

I do not understand your explanation on pointing pairs/pointing triples. In the example on the website there are 3s in B7 and B9 and you show that the 3s in B1, B2, and B3 can be eliminated. Why do you point left? According to the explanation is it not also possible you have pointing triplets of 3s (B1, B3, B3) that would point right. I would appreciate any additional explanation.

Regards,
Jerry

Andrew Stuart writes:
The 3s in C2 and C3 prevent the other 3s in B123 from pointing.

## ... by: Joe, Massachusetts

Thank you for the Sudoku Solver. I use it often on those super hard puzzles as a way to learn to use the more sophisticated solving techniques, and available with each step taken. It is easy for me to miss seeing them in puzzles with many possibilities in play. It is an invaluable tool for those who are good but not expert level. Thanks again.

Andrew Stuart writes:
Thanks Joe!

## ... by: unknown, far away

Hi
I'm totally new to this site, so please excuse me if this message is not relevant.
The solver indicates that the board below has 1 solution, but when i press the step button several times, the solver comes up with the error
ooops, error on your board, after incorrectly placing numbers against sudoku rules

where on your site can i read why this error happens ??

thanks
----
There is a Sudoku board I would like you to look at

http://www.sudokuwiki.org/sudoku.htm?bd=009040500010503060400290007020000103003010000190600048501007002200300700070120035

Andrew Stuart writes:
Ran that puzzle and it stepped through just fine.
Did you change the numbers manually at any stage?
"ooops, error on your board" suggests that, and it should highlight in red the conflicting cells

Andrew

## ... by: sundaresan, india

DEAR Mr.Andrew
WELL, THIS IS WONDERFUL.a complete one. I thankyou for the amazing guide opens all the doors. I donot think no more tips and tricks around.

thank you friend

sundaresan

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Thank-you everyone for all your questions and contributions.