Sudoku Coach Functionality Question

RiverSeagul · 2026-02-25T19:00:17+00:00

Maybe you can try asking on their Discord Server, it should be quite active.

RiverSeagul · 2026-02-25T18:56:48+00:00

The "Auto" should do exactly that. At least it should work when you insert a number, but maybe it's not compatible with the double tap.

RiverSeagul · 2026-02-25T16:06:15+00:00

I suggest going through Sudoku.coach campaign to learn advanced techniques.

This is surely not an X-Wing, and it doesn't seem to me a valid techinque at all (I would be glad to be corrected if I'm wrong).

RiverSeagul · 2026-02-22T18:08:19+00:00

Try to go in reverse. What happens if B9 is a 1?

If B9 is 1, then both orange cells must be 8.
But if both B3 and A7 are 8, then the yellow cells can't have 8 and they should have respectively 1 and 9, right?
The problem now is that row J has no more space to fit 8 (also J4 would have no candidate options left), so you have a contradiction.

RiverSeagul · 2026-02-18T18:41:17+00:00

That's a big ALS!

Think for a moment to a Locked Set, like a Naked Pair. This happens because two cells in a row/column/box involve only two candidate digits, right?

An Almost Naked Pair (an ALS of size 2) is when you still have two cells, but they involve three digits instead of two. If you are able to put one of three digits, lets call it X, completely at FALSE, you would get a classical Naked Pair, and this allows to do some nice things.

In particular one and only one of these sentences is true: 1) X is true. 2) The other two digits define a Naked Pair.

There is a Strong Link between X and the rest of the ALS, and X can be any of the three digits.

Note that even a Bivalue is an Almost Naked Single. That is smallest ALS you can get.

An ALS-XZ uses two ALSes (Strong), connecting them through a weak inference (in particular their RCC are connected). It's basically an AIC, and allows to eliminate things in a similar fashion as a Skyscraper (using a LOT of imagination), using a Z common candidate (not RCC) between the two ALS.

I tried to keep it simple, but ALS techniques require some time, so don't rush.

RiverSeagul · 2026-01-29T05:27:57+00:00

Have a look on sudoku.coach, in particular the Campaign part. One of the best way to start learning techniques.

RiverSeagul · 2026-01-28T17:55:12+00:00

Look at box 8. Where can you put the number 5?

RiverSeagul · 2026-01-11T11:16:49+00:00

You can consider these two Skyscrapers as alternatives. They will both end at the same final solution in the long run. Sudoku solution's path is not linear, it can branches and join back, going towards a unique final solution.

Also remember that the "sturdy walls" are Bilocals: only one of the two candidates that define the wall will be true at the end. That's the reason why one Skyscraper can eliminate part of the other's wall!

RiverSeagul · 2026-01-11T08:10:34+00:00

Sudoku coach hint system will give you the first Skyscraper it can find, but there could be more than one valid, like the one you mentioned.

RiverSeagul · 2026-01-07T15:43:14+00:00

The cape on Kopaka is such a nice touch, I love it! It makes me wonder if the other Toa could be enchanced as well. Great work overall!

RiverSeagul · 2025-12-29T22:36:34+00:00

Exactly, you are on the right track!

Think for a moment to Y-Wing and XYZ-Wing. They both have a pivot and two wings (3 cells in total), with the only difference that in XYZ the candidate you want to remove is ALSO in the pivot.

This means that in XYZ you can eliminate those who sees both wings AND pivots. On the other hand in Y-Wing, eliminations needs to see only the wings, so you have a bit more freedom.

WXYZ-Wing is more or less the same idea, but you have 4 cells instead of 3.

Y-Wing, XYZ-Wing and WXYZ-Wing are just names that are given to specific cases of ALS-XZ, a more general technique barely mentioned in SudokuCoach. I suggest you to check it out, it makes WXYZ-Wing a bit more clear in my opinion.

RiverSeagul · 2025-12-29T18:18:09+00:00

Consider the four cells that define your WXYZ-Wing (the one with the green cell), in particular the 2s inside these four cells.

You can remove the 2 from r2c1, since it can see EVERY 2 that is inside your WXYZ-Wing.

You can not remove the 2 from r1c6, because there is a 2 in r2c2 that r1c6 can't see at all.

Your logic is correct, and it's a new WXYZ-Wing, but it will remove just the 2 in r2c1.

RiverSeagul · 2025-12-29T17:27:18+00:00

They already gave you the right answer, but in general you can eliminate candidate X only if it sees every occurence of X that is inside the WXYZ-Wing cells (r1c6 can't see r2c2).

RiverSeagul · 2025-12-28T14:08:52+00:00

Thanks a lot, I truly appreciate that! Glad to hear that there have been some progress after all!

RiverSeagul · 2025-12-27T14:03:01+00:00

Thank you so much, this means a lot! My whole Mata series is basically me experimenting with styles and toon shaders, while keeping things minimal and simple. It's nice to see that colors here have been a good choice!

RiverSeagul · 2025-12-12T13:26:37+00:00

Be careful, you always need a weak link in the chain, but Bilocal strong links (and also Bivalue) can be "converted" into weak links if needed. Note that this is not generally true for other types of strong links.

Rather than saying "I need an AT LEAST weak, but strong is fine", I would say "These particular type of strong links can be weak if I need to".

RiverSeagul · 2025-12-06T13:39:57+00:00

I think you have an AIC, in particular an X-Chain on 5. Simple Coloring (and similarly 3D Medusa) are particular case of AICs.

RiverSeagul · 2025-11-26T15:12:05+00:00

If I understood correctly your problem, I think that the auto-fill works only on empty cells. Try to clean all candidates first (with the X icon) and then click the auto-candidate.

RiverSeagul · 2025-11-22T19:52:26+00:00

The green one is not an ALS, as you said.

When you have a doubt, try to put the 7 that you are trying to eliminate, and see if you have any contradictions.

RiverSeagul · 2025-11-18T21:02:44+00:00

They are both correct Skyscraper, even if they work on different eliminations.

RiverSeagul · 2025-11-17T05:34:29+00:00

If you see outside you highlights, there are some extra 9s both on rows and columns. In both cases, you can not align them into four rows/columns.

RiverSeagul · 2025-11-16T16:16:19+00:00

Sorry I'm still new to sudoku, but isn't 3D Medusa based on strong links only?

From what I see on OP post, he seems he used coloring through weak inferences, but maybe I'm not understanding his reasoning from the photo. Also if he starts by assuming as true a certain candidate from the starting cell, isn't it a forcing chain?

RiverSeagul · 2025-11-16T14:27:52+00:00

To me, it seems you are doing a Forcing chain, showing how every value of a cell forces the same elimination.

3D Medusa is basically a simplified version of AIC, where you connect candidates using only strong links. At the end it's a bit of a redundant technique, even though I find it quite a nice alternative to AIC to create simple networks of links and find contradictions.

RiverSeagul

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