# 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 andrew@str8ts.com.
**Post a Comment or Question here...**

## Sunday 10-Nov-2013

## ... by: Florent Chayet, France

Just one small remark: either the auto clear is on, and then when a solution is added all the previously manually suppressed candidates are back, either it is off and to suppress the candidates after adding a solutio is quite a job. The dream would be that auto clear on results in suppressing the candidates due to the added solution without changing anything else on the grid.

Thanks again!

## Monday 4-Nov-2013

## ... by: Hervé Gérard, France

Load Sudoku: CLICK TO LOADFirst of all, congratulations for your website that's to me the ultimate sudoku reference ever on the web!

Well I did not think I would have to do that but it seems to me there is a bug in the solver for the attached Sudoku. For some reason at step #11, the solver does not detect an obvious Unique Rectangle type 3 located CD45, the bi-value cell being D9 and thus eliminating candidates 6 in D1 and 9 in D2.

Instead the solver catches a hidden UR involving the same cells, which is fine. However the UR should have been logically tracked before.

The consequence in that case is 'dramatic' since it turns the Sudoku grade from tough to extreme! :-)

I am myself an IT programmer and I appreciate when bugs are submitted especially when the application is so elaborated and useful.

Thanks again for such an amazing tool!

## Sunday 3-Nov-2013

## ... by: David Eoll, New Hampshire, USA

Great site!! I'll be back....

## Sunday 3-Nov-2013

## ... by: Gerrit Altena, Netherlands

Load Sudoku: CLICK TO LOAD## Sunday 3-Nov-2013

## ... by: TomE, IN

However, in today's case, As I got futher into the step by step solution it turned out I had entered a number in the WRONG cell. I would like to go back to the beginning, make the correction and start over.

I have missed they way to do that. Or can you do that?

Thanks loads

TomE

## Sunday 3-Nov-2013

## ... by: Hassieb Wali, USA

I want to thank you for the most complete SUDOKU website you have developed and maintained. It is beyond my expectation and I often go to your website and seek help.

I have a question and have not been able to find a good answer and that is about X-Cycle: How do you find a X-Cycle and what are the criteria for it. Does it have to be bi-value? There is no reference in the X-Cycle definition you have provided,; however, your examples imply that they are bi-values. Also when you say: X-Cycle on 5, I see a lot of 5's that have been ignored and that is confusing. Could you help me a little bit with this problem. I would really appreciate.

Regards,

Hassieb Wali

I hope this is slightly helpful. Best is to look at examples found in the solver in the harder puzzles. They turn up a lot.

## Saturday 2-Nov-2013

## ... by: Ms Love, Florida

## Monday 7-Oct-2013

## ... by: doman, PL/BE

Load Sudoku: CLICK TO LOAD......5....4.18.9.3...79..6.6.9.2...795.8.243.......6...6.94.81..1..56......6....

Hidden Rectangle

rectangle: [A2, A8, C2, C8]

peak cell: C8[12]

conclusion: 2 strong links on 1 in peak cell

=> removing [2] from A2

## Friday 4-Oct-2013

## ... by: guru, India

Load Sudoku: CLICK TO LOAD## Friday 4-Oct-2013

## ... by: Svavar Kjarrval, Iceland

Load Sudoku: CLICK TO LOADHowever, when I put the numbers in without the last one (2 in bottom-right corner) the solver mistakenly thinks that number must be 3 and after that makes mistaken assumptions. I understand that the solver might not be able to figure out a solution but a wrong number leans towards a wrong strategy or a wrong implementation of it. Just thought you should know.

## Tuesday 1-Oct-2013

## ... by: reoiutporewiu, home

Load Sudoku: CLICK TO LOADThe puzzle does require (fairly extensive) backtracking to solve but it has only one solution.

The key point at which is fails appears to be in applying the Grouped X-cycles deduction rule. Disabling those rules and going straight to Solution Count fails with the error that it needs at least 17 givens. That's the minimum for normal Sudoku. The minimum for Sudoku X is no more than 12 (the URL above).

Thanks for this email. I've corrected the message to say 12 clues, but I'm afraid the server will not return a solution count with so few clues. I have to throttle the services since it's a busy machine and the brute force tester sucks CPU. I can confirm my offline solver finds one solution. I have an article about this puzzle.

I'd be interested in the first move you found for Grouped X-cycles. Would be nice to make further progress in that area.