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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. Please feel free to drop me a note on the side of the page or try the Facebook comment box. Or you can email me directly at .

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Email Address (optional) so I can reply directly if necessary (it will not be displayed here)

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: Please enter theletters you see:
Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

## ... by: Hache, France

Hi there,

Using the grader, the puzzle is rated moderate 79 but it contains an X-cycle which I have not yet got my head around. How does it rate at only moderate?

Thanks

Hache

Andrew Stuart writes (21-Oct-2012):

Some puzzles are relatively easy but also possess one bottleneck that requires a hard strategy to get through. My generator marks these sort of puzzles as undesirable to publish and I filter them out. The scoring is based on a) the number of rounds which is a measure of the number of opportunities to solve anything at any one time and b) the scores of each strategy used (plus some heuristic modifiers). So the grade not about which one hard strategy is used - in this case I think the X-Wing bumped it over from easy to moderate - but the overall accumulation of score parts.
More here if you are interested:

## ... by: Shari, USA (Ohio)

I am still learning many tips/techniques, thanks so much to your website, very helpful. My question is regarding the Y-Wing strategy. I understand the concept when the three cells form a perfect square (with the inclusion of the cell where you are eliminating a candiate. I get confused if the cells do not align in a perfect square. If the 3 cells are "mis-aligned" (as in Y-wing example 1 and example 2), how do you know which cell to label as "AB"? It seems as though if you label the three cells incorrectly, you may be eliminating the incorrect candidate from incorrect cells?
Thank-you,
Shari Tuttle

Andrew Stuart writes (20-Oct-2012):

Y-Wings that form rectangles take advantage of rows and columns but we're fortunate with Sudoku (as opposed to say Magic Squares) that we can also look across the 3x3 boxes for connections - giving us more chances but at the cost of having to look beyond rectangles. As long as the pivot cell AB can see both of the 'pincer' cells. Not every valid formation will lead to an elimination. You just need to scan the possible arrangements, see if the three cells contain pairs that connect like AB and C and then look at the forth squares. As long as the Y-Wing rules is followed through correctly you can apply the elimination.
Hope that helps a bit : )

## ... by: Sonja, Germany

Hi Andrew,
your brilliant site already helped me tons to keep my sanity - thanks for that!
Now I've got a problem - I can't get my head round an alternating inference chain which your excellent solver offers as a solution. To my mind, there's a logical inconsistency in it: It seems to colour two sixes in the same unit in the same colour without apparent reason, plus it seems to ignore another cell in that same unit, and ONLY due to this, a logical inconsistency in the box next to it occurs, leading to the six having to be placed in J6.
Now, the disconcerting bit is that the solution is right. But as long as I'm convinced that it's not actually the one logically necessary conclusion, I just can't go with it.
I've taken a screenshot - would you feel up for helping me with this problem?
Best regards
Sonja

Andrew Stuart writes (20-Oct-2012):

I'd love to see the puzzle. Can you use the "Email This Board" and copy/paste whats in the pop up. Then I can advise.

## ... by: Jack, New Zealand

Have been using your app on my iPad. The camera mode could be improved. Look at :) Sudoku +. Also, the ability to write on the screen, and thus follow a trail of pairs, employ colouring, etc, would be great. Look at Astraware's SudokuOTD. Otherwise, your solver is best of a large bunch. Thanks.

Andrew Stuart writes (15-Oct-2012):

I'll take your hints and have a look at those, thanks for sharing. Oliver and I are both keen to keep improving the app and we're hoping to release an update very soon. So I'll add your ideas to our wish list. I've been thinking about the colouring of pairs on the website version. It's tricky to avoid over complicating the UI but t would be a useful facility for finding chains.

## ... by: Jolan, Britain

Just discovered your excellent site and am VERY interested in acquiring your book (so are many of my friends). HOWEVER, I have just read the three reviews on Amazon.co.uk and ithe all agree there are many errors in the copy they purchased.

My main interested would be clear explanations of some of the advanced techniques (x-cycle discontinuous alternating nice loop, etc).

Has there been a revision? THANK YOU for the really brilliant site.

John

Andrew Stuart writes (2-Oct-2012):

I have a page for corrections, do have a look at:
/The_Logic_of_Sudoku_Resources_Page
and apart from the odd typo, there's not too much to complain about, I think. One of the diagrams I actually insert into the book.
If you like the writing style on the site you'll find it similar, if a little chattier, in the book.

We had the proof done very well but then the publisher said I could have fifty extra pages for no extra cost, so I added another chapter and some more puzzles and of course that didn't get proofed - so pros and cons really. The whole sudokuwik.org compliments and extends what is in the book and it's like a big place I can keep readers up-to-date. Also, I am thinking of creating an ebook version which could be ready next year.

Hope that helps

## ... by: Peter, USA

Thank goodness I found this site today! Learning the simple coloring strategy has saved me from certain insanity. You have my gratitude.

Andrew Stuart writes (1-Oct-2012):

Thanks Peter!

## ... by: Alan, Uk

Hi
Your iPad app seems to have a problem reaching the Internet to load new puzzles. I have noticed this for a few days. Trying later in the day seems to work. Today the problem is persisting. Internet is working fine and all other apps ok
Thanks

Andrew Stuart writes (26-Sep-2012):

The puzzles are picked up using our main domain name str8ts.com but the address resolution is failing. Zoneedit manage this for us but either a) they are incompetent (trying to move stuff or convert to IPv6) or b) under a DoS attack. Their status and customer feedback are non-existant. I've found a few tweets on https://twitter.com/zoneedit. To fix this I'm moving ISP which may cause some addition downtime but at least I'll be in control and can monitor progress

## ... by: Photospiration, UK

Kenken won't connect to the Internet to download today's game, neither will the app I bought from you load today's puzzles.

Is there a glitch?

Andrew Stuart writes (26-Sep-2012):

Yes but not with the app. The puzzles are picked up using our main domain name str8ts.com but the address resolution is failing. Zoneedit manage this for us but either a) they are incompetent (trying to move stuff or convert to IPv6) or b) under a DoS attack. Their status and customer feedback are non-existant. I've found a few tweets on https://twitter.com/zoneedit. To fix this I'm moving ISP which may cause some addition downtime but at least I'll be in control and can monitor progress

## Sunday 16-Sep-2012

Tried the Killer Sudoku solver. There seems to be a requirement that each cell is assigned to a cage. This is not always the case.. I think you need to remove this requirement.

Great book btw.,

Andrew Stuart writes (17-Sep-2012):

Yes, Yesterday I patched the Killer solver to cope with correctly clued boards - in some cases it was causing the solver crash. I thought you were pointing out a problem with single cell cages but I've tested them, seem okay. Do you have an example? Can you use the "Email this board" to send to me..

## ... by: Dan, England

I am trying to use your kenken and kendoku solvers on Internet explorer 9 and when I click either "Grader" or "Take Step", I get the following message: Solvers have been updated to version 1.89!

Andrew Stuart writes (10-Sep-2012):

Very sorry about that, my last upgrade - I should have incremented the version numbers in those solvers as well. Refresh today, should be back to normal now

## ... by: Dorita, California

I see you have an app in the iTunes store. Any chance of an Android app? I love the puzzles here and it would be great to have them on the go.

Andrew Stuart writes (10-Sep-2012):

I very much want to make an Android version, but struggling to find a decent developer at the moment. I'll certainly post an update on the site when I make progress. Glad you like the puzzles!
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