Three different questions?

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berni
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Three different questions?

Post by berni » Sun 06 Jan, 2019 4:02 pm

In my oppinion, we've got at least three different questions here. I would be happy, if we could segregate them a little:
  1. Which variation is considered a valid sudoku variation? (Killer is, Latin Square or Starbattle is not, but where are the borders...)
  2. How do we cope with difficult solving techniques? (See discussion of the very hard standard sudoku, which in my oppinion should not be limited to standard sudoku.)
  3. When do puzzles (sudoku variations) feel like sudoku and when not? (This has been addressed by the Indians in the WSC/WPC 2017 with the two Is-It-Sudoku-Rounds.)
While a) and c) are questions, that only concern sudoku contests, b) might also tangle other puzzles.

In my oppinion it's not possible (or at least not wishable) to give a clear border, but to let organizers have some freedom here. Anyway, one could give some corner points, so organizers have something they can hold on to.

detuned
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Re: Three different questions?

Post by detuned » Sun 06 Jan, 2019 6:39 pm

My thoughts so far:

(a) Which variation is considered a valid sudoku variation?

I don't think this question makes sense as stated in terms of something being valid or not. I'll try and expand upon this a little more however in terms of what I've heard so far. I have a lot of time for Thomas's suggestion that you have Sudoku, Sudoku Variants, Puzzle-Sudoku Hybrids and Not Sudoku, as a starting point, however, the question about how we separate Sudoku Variants and Puzzle-Sudoku Hybrids is not easy, and I'm not 100% convinced yet this is definitely the best way to think about things. More on this in question (c).

So I think this question is better stated as when can a puzzle be genuinely classified as "Not Sudoku". To begin to answer this I think we need a list of criteria of things that Sudoku definitely need to have.

For example, we definitely need to have a 2-dimensional grid of cells, each of which belongs to (at least) 2 rows/columns and also belongs to a region (a marked group of cells which do not trivially intersect with the rows/columns). We then definitely need to place symbols into this grid. (This is obviously incomplete, I just wanted to make an example).

It is likely that this list "should" apply to all Sudoku Variants, and probably also to some Puzzle-Sudoku Hybrids. This probably isn't going to be entirely satisfactory, but again I think further clarification and guidance is better thought about in question (c).


(b) How do we cope with difficult solving techniques?

My initial reaction to this is that it isn't strictly a relevant question. I certainly have some sympathy with the point of view which says this isn't really a problem of definition - I suppose the reason for including the hard classic as an example was driven by the questions asked in the polls: "Is this suitable for a sudoku competition?" As I've mentioned elsewhere, in the absence of a clear definition, this question I think is easier for people to answer consistently, and for me to be able to interpret more consistently.

Anyhow, the topic has generated some good discussion. From my own point of view, I can't see that it is yet helpful with regards to definitions and classifications, but I'm happy to keep exploring this in case it does reveal something. Certainly one answer to this question is to trust in the judgement of competition organisers and their testing processes.


(c) When do puzzles (sudoku variations) feel like sudoku and when not?

So here we fundamentally need to address what is a Sudoku Variant, and what is Puzzle-Sudoku Hybrid. Again speaking personally I'm not quite sure about this :-) or even if it's possible to be absolutely sure one way or the other :-)

The Indians in 2017 certainly expressed a clear point of view, but I do not think it has been adequately explored yet. Speaking personally, I also do not believe their experiment was particularly successful either - I think there was much in the WSC round which I thought controversial. I've also thought about things the other way around. I'm not sure the equivalent WPC round was entirely successful either - or perhaps popular is a better word. There are certainly a number of WPC solvers who have a certain animosity towards anything that looks like Sudoku, regardless of how it solves. These solvers would argue that because there is a separate WSC, even the most spurious Puzzle-Sudoku hybrid has no place at the WPC. This seems strange to me, because Sudoku is a type like any other, and it's not like there aren't other puzzle types which are staples at the WPC which have spawned many variations - Tapa, Fillomino, Snake, Kakuro immediately come to mind (I'm sure there are many more) which theoretically you could produce a series of rounds of variants to produce some kind of championship.

This way of thinking kind of leaves the more controversial of our Puzzle-Sudoku hybrids in no-man's land.

Returning to the question, this is going to be the most difficult thing to agree on - different people are going to have different answers about how they feel about this. I've used the ideas of Sudoku Variants and Puzzle-Sudoku hybrids throughout this post, however I'm not convinced it's the best way to think about it. I think my approach is going to (eventually) involve a rigorous classification of additional constraints that you can add to a Sudoku. You can add more than one constraint at a time which is what make things interesting.

An initial example of how I'm thinking goes something like this:

- One family of constraints are the addition additional regions where numbers are not allowed to repeat. This covers things like diagonals, extra regions, but also cages like Renban and Killer. I think, after the example set in 2016, we have to think like this. For those that don't recall, there was a round in this WSC where an Extra Regions puzzle was presented using the rules of Killer, and a Windoku puzzle was presented using the rules of Renban.

- Another family of constraints impose constraints based on the arithmetic properties of how some numbers to be placed grid compare and combine with other numbers to be placed the grid, and require a certain amount of calculation to resolve. This covers things like sums, products, differences (in particular differences of 1 give you a consecutive constraint), ratios. It probably also includes things like whether one number is smaller, bigger or equal to another number. It might even include whether numbers leave a remainder of either 0 or 1 when divided by 2.

From this point of view:

- Diagonal is an additional non-repeating area variant
- Consecutive is an arithmetic variant (in this case with the arithmetic constraint applying to every pair of adjacent cells)
- Killer is both an additional non-repeating area variant, and an arithmetic variant.

This is only a start, and even as I type it doesn't seem entirely satisfactory to me. For one thing, the arithmetic constraints need to have a well-defined domain of application. This might be rows/columns (e.g. Skyscrapers), this might be pairs of cells (e.g. Consecutive), this might be 2x2 areas of cells (e.g. quad max), this might combine with additional grid decorations (e.g. Arrow), it might combine with non-repeating cages (e.g. Killer), and there's plenty more to think about there for sure.

Once you have something rigorous, maybe it will be easier to more precisely draw a line between what feels like Sudoku and what doesn't.

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Re: Three different questions?

Post by Fred76 » Mon 07 Jan, 2019 9:52 am

berni wrote:
Sun 06 Jan, 2019 4:02 pm
In my oppinion it's not possible (or at least not wishable) to give a clear border, but to let organizers have some freedom here. Anyway, one could give some corner points, so organizers have something they can hold on to.
Why do you say it's not wishable to give clear border? I think the exact opposite: without clear border, what is the meaning of being world sudoku champion?
As you come from Germany, and I've taken part in a few german sudoku championships (DSM) (and have played a few others at home), I would like to take this example.
I feel that all puzzles appearing in DSM are inside clear borders: no repeated digits, no blank cells in solution, regions of size N where N is the number of distinct symblos to be placed, etc... I can't remember a single puzzle that is outside these clear borders. Thus my questions: do you think DSM is a poor competition in term of author's creativity? Do you think LMD should ask other authors to have more diversity in DSM? If not, why do you think it's not wishable for wsc? what is the difference between these 2 sudoku competitions that require clear limits for one and no limit for the other?

Fred

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Re: Three different questions?

Post by berni » Mon 07 Jan, 2019 10:32 am

Fred76 wrote:
Mon 07 Jan, 2019 9:52 am
Why do you say it's not wishable to give clear border? [...]
no repeated digits, no blank cells in solution, regions of size N where N is the number of distinct symblos to be placed, etc... [...]
I first of all I said, it's not possible. But if you think it is, can you just define it, like you think it should be? The one you sketched contains "etc..." which makes it a non-clear definition.

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Re: Three different questions?

Post by Fred76 » Mon 07 Jan, 2019 10:40 am

berni wrote:
Mon 07 Jan, 2019 10:32 am
Fred76 wrote:
Mon 07 Jan, 2019 9:52 am
Why do you say it's not wishable to give clear border? [...]
no repeated digits, no blank cells in solution, regions of size N where N is the number of distinct symblos to be placed, etc... [...]
I first of all I said, it's not possible. But if you think it is, can you just define it, like you think it should be? The one you sketched contains "etc..." which makes it a non-clear definition.
I will do a list of criteria I think important for sudoku, let me some few days to try to do it the clearer way possible.

Fred

Realshaggy
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Re: Three different questions?

Post by Realshaggy » Mon 07 Jan, 2019 11:27 am

As you took DSM as an example, I think it's important to know why these contests are like that: These have been authored by basically the same group of people for the last twelve years. In the first years, Stefan was the head of authors and Richard provided a big chunk of the puzzles. In the last years, Richard was the head of authors. (And not to forget, Arvid also provided lots of puzzles and also some more occasional authors.) Among these, Stefan has a very strict opinion of what Sudokus should be in a competition. In the first years, each Sudoku was 9x9 with 3x3 boxes, the first "Irregular" is from 2012 and they still are a very rare occurence. I don't remember if there ever was something else used than numbers 1-9, let alone double symbols or other things in the grid.

But all that, and thats the important part, was at the decision of the authors team, just as it is the case for WSC. To my knowledge there have never been restrictions by LMD (as the WPF representative) regarding the puzzles. Only small suggestions, based on experience what went good or wrong from year to year, and that was more for things like playoff structure.

In my opinion, it also never felt necessary to intervene. (And thats also the case for the puzzle competition counterpart where we had like 25 different main authors in the last 10 years, who sometimes provided very innovative ideas.)

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Re: Three different questions?

Post by Fred76 » Mon 07 Jan, 2019 11:47 am

I took DSM as an example, but I could have taken UKopen sudoku tournament or Polish sudoku championship, too. In both cases there were much more authors who contributed than for DSM.
I could also have mentionned India, with the notable exception of WSC2017. But as we can see now, none of the sudoku competition they organized before and after the WSC 2017 looks like WSC 2017 concerning puzzle types. So I ask myself what was the purpose of this strange experimentation...

berni
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Re: Three different questions?

Post by berni » Mon 07 Jan, 2019 1:20 pm

detuned wrote:
Sun 06 Jan, 2019 6:39 pm
For example, we definitely need to have a 2-dimensional grid of cells,
When I read this, I remembered as sudoku from 2006, which was 3D and which might qualify as sudoku... I put it in an own thread.

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Re: Three different questions?

Post by Fred76 » Mon 07 Jan, 2019 1:48 pm

berni wrote:
Mon 07 Jan, 2019 1:20 pm
detuned wrote:
Sun 06 Jan, 2019 6:39 pm
For example, we definitely need to have a 2-dimensional grid of cells,
When I read this, I remembered as sudoku from 2006, which was 3D and which might qualify as sudoku... I put it in an own thread.
Or the 2011 WSC round 12, which consist of a real cube (not a 3D representation on a 2D paper).

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Re: Three different questions?

Post by DavidC » Mon 07 Jan, 2019 11:36 pm

"Or the 2011 WSC round 12, which consist of a real cube (not a 3D representation on a 2D paper)."

I feel that anything involving physical handling/dismantling/constructing/manipulation is a distraction and a gimmick.

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Re: Three different questions?

Post by Fred76 » Tue 08 Jan, 2019 10:32 am

DavidC wrote:
Mon 07 Jan, 2019 11:36 pm
"Or the 2011 WSC round 12, which consist of a real cube (not a 3D representation on a 2D paper)."

I feel that anything involving physical handling/dismantling/constructing/manipulation is a distraction and a gimmick.
I generally agree with that, but round 12 of WSC 2011 is for me a kind of exception: here I feel the idea was good, it's natural to have a 3D puzzle which is to be solved in 3D. I felt it's not an artificial gimmick.

I would add that I feel that the kind of very special rounds that occur sometimes in WSC are generally big fail from my point of view, for 3 reasons:
  • Sometimes I feel strongly they are not sudoku, and if the result of this commitee can fix this point, it would be a first big step
  • Most of the time, I feel these rounds are overvalued compared to the rounds containing more conventional puzzles
  • This is subjective, but it's rare that I find the kind of puzzles of these rounds are enjoyable
Exceptions to that were WSC 2011 round 12, as I said. I can also mentionned the tredoku round of WSC 2016, even if I didn't take part. I feel this is a round that I could have enjoyed.

If you add 2 more points to the 3 points mentionned above: you weren't able to solve it and you see your final rank more than doubled thanks to it, it's enough for the most enthusiastic player to give up to invest time, energy and money to take part in future wsc. Among all these points, the fact the puzzles are not sudoku was kind of eliminatory for me, I can live with frustrations coming from other points.

Fred

detuned
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Re: Three different questions?

Post by detuned » Tue 08 Jan, 2019 12:28 pm

Maybe we need a separate topic for Isometric Sudoku (or Penrose Sudoku and so on). They may look like 3D puzzles, but there is absolutely no need to consider them in anything other than 2 dimensions. That round in Eger in 2011 could very easily have been conceived using 3 flat hexagonal pieces of card/paper.

I'm not sure the committee is going to have very much to say about gimmick one off rounds at WSCs, beyond whether the puzzles they involve can reasonably be considered as Sudoku.

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Re: Three different questions?

Post by Realshaggy » Tue 08 Jan, 2019 12:40 pm

I think, this is going a bit far from the question of the topic, but if we are already at discussing round concepts and big special rounds:
I only remember a few examples, where these rounds were overvalued, and these examples probably are outliers because the top solvers were even fast than expected and got a very high time bonus.

But there are some more things, that I think are really bad about that special rounds or big combo-rounds: they tend to have a very high variance and proper timing is very difficult, especially across skill levels.

The majority of the solvers get's a whopping zero points and I'm always one of them. It's very frustrating for me. Also for the top solvers, it's probably not a good experience. They know, that usually a large portion of their points comes from a time bonus. So they feel, they have to rush and there are always disappointed people, who essentially solved the puzzle but get a zero point round because of a very small mistake.

Partial points do not always solve this problem. I remember the "olympic rings" round of five connected classic sudokus from Beijing. When re-solving the puzzle, I learned that these could be solved one by one if you started from the right. Instead, I started from the left, solved the first four up to a small ambiguity and got nothing.
At the last DSM in a combo-puzzle instead of the planned entry I found a different one in the opposite corner. Progress was slow but still feeled reasonable, so I did not think about a different starting point. At the end, large parts where solved, but no part without a remaining ambiguity and again, zero points for me.

So this is also subjective, but I agree with Fred in that case: these rounds are not enjoyable in a contest for me.

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Re: Three different questions?

Post by Fred76 » Fri 11 Jan, 2019 6:16 pm

berni wrote:
Mon 07 Jan, 2019 10:32 am
Fred76 wrote:
Mon 07 Jan, 2019 9:52 am
Why do you say it's not wishable to give clear border? [...]
no repeated digits, no blank cells in solution, regions of size N where N is the number of distinct symblos to be placed, etc... [...]
I first of all I said, it's not possible. But if you think it is, can you just define it, like you think it should be? The one you sketched contains "etc..." which makes it a non-clear definition.
Here is a text which could be my definition of sudoku, at least I think all criteria are the things about which we are debating here.
I'm not completely satisfied with the formulation, at least point 1.1 is not very clear but I think I've at least demonstrated that it is possible to define clear borders.

A sudoku is a grid-based puzzle whose goal is to fill cells with a set of N distinct symbols and which fulfills the following conditions :

Structure of the grid :

1.1 There are at least three types of sets of cells which satisfy conditions 1.2, 1.3, 1.4 and 1.5 : two directional types of sets called rows and columns (rectangular grids) or generalized rows (other geometries) and one type of sets called regions, each region being formed by connected cells belonging to at least two distinct rows and two distinct columns, or two generalized rows of each direction.
1.2 All cells must belong to at least one row and one column (rectanguar grids) or two generalized rows (other geometries).
1.3 The set of regions must cover at least 75% of the grid (75% of cells).
1.4 Each row, column and generalized row must contain exactly N cells.
1.5 Each region must contain exactly N cells.

Any solution must meet the following conditions :

2.1 Each row and column must contain each symbol exactly once.
2.2 Each region must contain each symbol exactly once.
2.3 Each cell can contain only one symbol.

3.1 The placement of the symbols in the grid is the complete solution of the puzzle.


A few comments:
1.A definition of generalized rows that works for each geometry is still missing (I'm quite sure I've seen that in the past, but I can't remember where).
2.I'm not entirely against a relaxation of some points. For example, primrose and star sudoku don't satisfy condition 1.2.
3. I tried to avoid a maximum of arbitrary factor, but I've set a 75% in point 1.3, to incorporate 9*9 irregulars with 1 or 2 regions being actually rows or columns. I feel this way is a good compromise, so that a 9*9 sudoku with usual 3*3 boxes can't have less than 9 regions (if you have 7 regions, the cells not contained into regions form 2 regions automatically).
4. Some clarification about what are cells is perhaps needed (for example, what I call "cell" for a tight fit sudoku can be half squared).
5.Regions: "Connected cells" can be clarified, too. In my opinion orthogonally, diagonally (->chain sudoku), and toroidally (sudoku toroidal) connexions are ok. In scattered sudoku (see for example here: http://sudokuvariante.blogspot.com/2011 ... ku-n1.html) the "scattered" region is not a region as defined here, but it's ok because we still have 8 other regions which are ok with the definition.
4. It's intentionnally that I didn't write that the puzzle needs a unique solution: I wanted to leave space for linked sudoku, or relay consisting of several sudoku with each single sudoku having several solutions, and secondly for just one cell sudoku, which is a classic sudoku with several solutions. This point of uniqueness should be clarify somewhere.

I don't think this definition is perfect, but if it can help for further discussions, I would be happy.

Fred

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Re: Three different questions?

Post by detuned » Sun 13 Jan, 2019 12:43 pm

Thanks for the post Fred.

On 1.1 - I'm not sure we need to get too technical with the definition of regions. The guiding principle should be that the regions are clear and well described, and I think trying to reach a level of abstract generalisations which covers a whole range of the cases isn't necessarily going to add much practical value. What's the point of a definition if no-one understands or uses it?

1.2 to 1.5 are interesting. In 1.3 we have a clear compromise defined, with respect to cells belonging to regions (although I think this is badly conceived). In 1.2, you are willing to maybe compromise, and 1.4/5 there is no room for compromise. Is there any reason for this? For instance, you talked about Penrose and Star with respect to 1.2 in that there are some cells which are not double checked by generalised rows. Maybe one acceptable relaxation of the rules is that if you do have such cells, then you are only allowed one per region. On the other hand, the rigidity of 1.4/5 and the "exactly once" phrasing rules out examples like blackout, surplus and deficit. Is there no equivalent controlled relaxation of the rules that might apply to 1.4/5?

With specific regards to 1.3, I think we really need to nail down that each cell must belong to a region. The problem you are talking about is where regions and rows/columns exactly overlap, and so you are actually talking about two separate points with this item.

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Re: Three different questions?

Post by berni » Mon 14 Jan, 2019 10:58 am

Ignoring the fact, that I'd not demand distinct symbols, I can go along with 2.[123] and 3.1. But I think you do in 1.1 through 1.5 a huge effort to avoid bare latin squares. Is this really necessary?

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Re: Three different questions?

Post by Fred76 » Mon 14 Jan, 2019 11:55 am

berni wrote:
Mon 14 Jan, 2019 10:58 am
Ignoring the fact, that I'd not demand distinct symbols, I can go along with 2.[123] and 3.1. But I think you do in 1.1 through 1.5 a huge effort to avoid bare latin squares. Is this really necessary?
I think what makes a latin square to be a sudoku is regions, which ideally cover the whole grid and must contain same set of symbols than rows and columns.
I don't feel it's a good idea to weaken the regional constraints, because in my opinion that's the most important property of sudoku.
It's perhaps subjective because I just think bare latin square is a very boring puzzle type: just about checking rows and columns, while adding regions can provide much more interesting logic. In my opinion interesting latin square puzzles come from additional constraints: kropki, skyscrapers, sudoku, etc...
But if latin square is a sudoku, then we've to revise the whole sudoku history...
On the other hand, I think it's important for a square grid sudoku to be a latin square. (I just want to notice here that latin square is something that is pretty well defined and it seems to me that nobody would say about a puzzle containing repeated digits that it is a latin square. On the other hand kropki, skyscrapers, classic sudoku are latin square puzzle with more constraint, for me they are latin square variations. I don't know why we couldn't do the same intellectual construction with sudoku: "classic sudoku is well defined puzzle type, with well-defined properties. sudoku variations are the puzzles that have same properties with more constraints").

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Re: Three different questions?

Post by Fred76 » Mon 14 Jan, 2019 12:19 pm

detuned wrote:
Sun 13 Jan, 2019 12:43 pm
On 1.1 - I'm not sure we need to get too technical with the definition of regions. The guiding principle should be that the regions are clear and well described, and I think trying to reach a level of abstract generalisations which covers a whole range of the cases isn't necessarily going to add much practical value. What's the point of a definition if no-one understands or uses it?
I agree this is not well written. On the other hand I think it's important to say that regions is composed of cells that are connected. A whole new branch of puzzle type will open if you say only that regions are clear and well described, and I'm not sure everybody will say these new puzzles are sudoku.
detuned wrote:
Sun 13 Jan, 2019 12:43 pm
1.2 to 1.5 are interesting. In 1.3 we have a clear compromise defined, with respect to cells belonging to regions (although I think this is badly conceived). In 1.2, you are willing to maybe compromise, and 1.4/5 there is no room for compromise. Is there any reason for this? For instance, you talked about Penrose and Star with respect to 1.2 in that there are some cells which are not double checked by generalised rows. Maybe one acceptable relaxation of the rules is that if you do have such cells, then you are only allowed one per region. On the other hand, the rigidity of 1.4/5 and the "exactly once" phrasing rules out examples like blackout, surplus and deficit. Is there no equivalent controlled relaxation of the rules that might apply to 1.4/5?
I'm not completely against relaxation of 1.4/1.5 (I said it in the post).
I wanted to have the less possible subjective factors, that's why I didn't write the relaxed rules first. If you want to have the most objective definition, then 1.2, 1.4 and 1.5 are fine, in my opinion. All kind of relaxation of these rules will force us to define subjective limits that will be hard to impose on everyone (because everybody will argue they are subjective).
I took example of relaxation of 1.2. because I've more sympathy for it. Let me explain why: In the examples I took I think the relaxations come from geometry of the grid. If you want to adapt at best the sudoku rules in a primrose grid, you then have to adapt a bit the strict definition.
In the examples you took: blackout, surplus and deficit, the relaxation doesn't come from an external factor like geometry, it comes from the author himself who decides to change these properties.
detuned wrote:
Sun 13 Jan, 2019 12:43 pm
With specific regards to 1.3, I think we really need to nail down that each cell must belong to a region. The problem you are talking about is where regions and rows/columns exactly overlap, and so you are actually talking about two separate points with this item.
I agree with you that the whole 1.1-1.5 should be formulated in a much clearer way.

I forgot in my rules that regions should not overlap.

Fred

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