Tuesday 11 April 2017

2017 Sudoku GP: Round 4 United Kingdom

First off - the last couple of weeks of Friday Puzzles have been delayed for one reason or another.  Hopefully I can catch back up this week and post 3 puzzles this coming Friday.

Secondly, although I have been quite free with my opinions about this year's Sudoku GP thus far, if you think I have the temerity to rate my own puzzles - then you have another thing coming, dearest reader.  Nevertheless, I thought it'd be worth offering an author's (rather than ex-director's) view on this round's puzzles, which I co-authored with my good friend/bitter solving rival, David McNeill.

1-6 Classic Sudoku (25, 17, 20, 25, 47, 30 points)

So I hope this represented a decent selection of classics.  Certainly no puzzle was what I'd call a guessing puzzle.  David's were puzzle 2 and 6, the rest were mine.  Puzzle 1 is probably a lot easier if you start by placing all the 1s, then the 2s and so on.  This is a standard nikoli gimmick for easy puzzles that I like to throw out every now and again.  It works better if you aren't necessarily expecting it; over using it wears thin very quickly.  5 was the hardest, perhaps notable because it needed a few naked singles to get going.

7 Diagonal Sudoku (31 points)

David's puzzle - not sure there's too much to say other than a pleasant enough Diagonal puzzle

8 Antidiagonal Sudoku (33 points)

Mine (and I prefer Anti-Diagonal) - This was nearly a very good puzzle of 16 givens, but I couldn't quite get it to solve uniquely.  I'd have persisted with this a lot longer had this been say, for a world championships.  This would have fitted in well with a couple of other 16 given puzzles in Round 2 of the 2014 WSC, and might be something I end up revisiting.  Watch this space.

9 Windoku (58 points)

Mine - I really quite like Windoku as a type, with its 4 visible extra regions and additional 5 implied extra regions.  At first glance you might think I was going for another 16 digit puzzle and had to add another given in the middle to get to 17, but no, that's not what I was going for this time.  Perhaps the more observant of you will have noticed the centre 9 givens form a magic square?  Anyhow, a reasonably tough windoku, as far as these things go, but I suppose if you've done a few of my puzzles you'll have got through this steadily enough.

10 Antiknight Sudoku (36 points)

David's (and I prefer Anti-Knight) - I suspect he was going for a 17 given puzzle here and had to add the corner givens to get this out uniquely.  Other than that, a pleasant enough Anti-Knight solve.

11 Disjoint Groups Sudoku (56 points)

David's - I always think that half the issue with disjoint groups sudoku on paper is visualising each of the 9 disjoint groups.  When solving I often have to draw shapes in the cells to help with that.  This puzzle has a nice UK theme, and is potentially a tricky solve if you struggle to visualise the groups, but if you are comfortable with the type I think solves quite nicely.

12 Irregular Sudoku (40 points)

David's - the temptation with nicely designed irregular puzzles is to push the difficulty to an extreme, or else to go to extremes using the grid's geometry to shape the solve.  I think David hit a nice medium here - the first comment I gave when testing this was that I assumed a couple of the givens weren't strictly needed (in the sense that removing them would still give a puzzle that solved uniquely) and that it felt like an easy solve - but checking my time it was clear that this wasn't a trivial puzzle and instead the feeling that it had gone quicker is a reflection on how nicely the puzzle solved.

13 Renban Killer Sudoku (63 points)

David's - normally I'm sceptical about combining together too many rules, but the combination of Renban groups and Killer cages combines really nicely and I think David is really on to something with this variant, which he has made his own.  Another nice example

14 Cloned Strands Sudoku (33 points)

David's - I'm pretty sure David invented this type primarily to draw funny pictures of animals.  And a nice illustration that novelties don't have to (a) have overly complicated rules and (b) have overly difficult solving logic.

15 Total Blackout Sudoku (86 points)

David's - blackouts tend to have quite fiddly solving paths, so the gimmick with the sums of the cells around the cells helps to give this type a bit more flavour, as well as providing a nice pun for the variant.  I think most of the points value here comes from firstly the novelty value of the variant, and second of all the slightly fiddly bit of logic needed to resolve the top right of the grid.

Top 3 (preliminary results):
1. Kota Morinishi (850.3 points)
2. Tantan Dai (845.5)
3. Tiit Vunk (790.2)
It looks as if there is a strange result for 11th (Huxuan Yu) who has a lower points total than 10th, despite the fact he managed to solve the puzzles nearly 3 and half minutes faster, going by submission time.  It's my strong suspicion that this is another case of the failure of the claim bonus button, an issue that has been plaguing the GP for years, particularly for Chinese solvers.  I hope an appeal is made or someone notices this before the results are made final.

As for the Brits:
45. Heather Golding (478)
68. Mark Goodliffe (380)
99. Michael Collins (334)
Also good to see there was a relative strong UK turnout of 18


  1. The problem when you create a novelty that don't have overly complicated rules is that you can't be 100% sure it is really a novelty. Concerning Cloned strands sudoku, I created a variant with exactly same rules in 2011: (see here - my blog is no longer online: http://3.bp.blogspot.com/-4q85F4kzjyk/TuTRpsDKE4I/AAAAAAAAAYI/3mPKhccEJoo/s1600/same%2Bchains.png).

    I think the balance of this round was not good. Blackout sudoku doesn't follow strict rules of sudoku (to solve it you can't use the easiest technique that you use to solve a classic sudoku), so it is in my grey area - like deficit and surplus sudoku for example. I always accepted and will always accept small twist of sudoku rules, so blackout is ok as a variant for me, but I prefer when such puzzles are more discreet in the points distribution. The problem is the balance: I don't like when these kinds of puzzles have too much weight in a tournament. When these puzzles appear to be highest pointer of a tournament, I always ask myself what was the goal of authors (and sometimes you have some surprises when you discuss with authors). I know David and you, I want to think it is only a bad choice, no "political" position about sudoku. Now I only hope this is not a new start of the game "Which kind of non-sudoku puzzle can I create for a sudoku tournament?" It would definitely kill me ! (but I say again blackout sudoku is yet ok for me).
    That being said, and adding that I just hate blackout sudoku, I was surprised by the smooth solving path of this one. The sum rule adding some constraints to a variant which don't have enough to my taste.

    Otherwise, I think the quality of the tournament was very good. I enjoyed a lot the set of classics, probably the best one of sudoku GP this year. The variants were nice and fun, too.
    I'm happy to have solved all puzzles in 1h13. I think it is a good performance on this set. Of course this is not exactly true, as for online tournament, it means submit right codes, and I'm a bit angry against myself to be in a bad series of doing sh*t while entering codes (it already happens to me in 3rd round).


  2. Fred,

    Thanks for pointing out your nice puzzle. I'm happy to acknowledge that I wasn't first with this idea. I hope you liked the cute animals though.

    I felt the Total Blackout was over-pointed and it certainly wasn't my intention to make any of the novelties particularly hard.

    Well done on your performance in the test.


  3. So hopefully it's clear enough that the animals comment is a little tongue in cheek, as I know David enjoys creating them very much. I wasn't aware of your invention Fred, although I had come across the type before at a previous uk open competition.

    To address the comment of balance - I think what you are getting at here is more to do the points allocation, which the authors have limited influence rather than the balance of easy/hard puzzles. From the latter perspective I'm sure it wasn't perfect, but I don't think there were either too many easy puzzles or too many harder puzzles, and I think there was a reasonable mix in terms of the 'type' of variants. If you are more concerned with the points then that is a matter for Nikola.

    Finally I'm glad you enjoyed the classics, I think they form an often overlooked part of the competition but I think it is very important to get right as this is what the majority of less experienced solvers will be solving.

    1. My comment about balance was not about points allocation.
      It was specifically about the fact that the hardest (according to testers) puzzle is by nature a bit different from sudoku (see more detailed answer on the comment below).
      I don't care much about points allocation on GP, but I think in my experience it was ok here.
      The blackout is a special puzzle. I think that some sudoku solvers skills can be transposed to solve this variant (mainly solvers who concentrate the solving on "what can be the content of a blank cell or set of blank cells"), while some other skills cannot be transposed and can make this variant a bit painful (solvers who concentrate the solving on "where a digit or a set of digits can be placed").
      I'm clearly in the second category of solver, hence for me the total blackout was the hardest puzzle of this round.
      I agree that probably for other players it was not the hardest puzzle of the round.


    2. You are talking about the opinions of the testers, so this is precisely a matter of points allocation. I'm not sure there is anything else the authors can tell you, when you yourself have stated you enjoyed the puzzle and thought it had a smooth solving path.

      I think your starting point is that of a fundamentalist and I think your views are overly conservative if you think submitting this puzzle for editorial consideration for inclusion for a competition was a bad decision on the authors part. I'll discuss more in the other comment later.

  4. And to address blackout - I take the point about a grey area perhaps, but I think this is more a matter of taste. Other solvers don't like mental arithmetic as much, for example, and are often dismayed to see high point killers. I don't think the answer here is to shy away from any controversy. You have to give the authors a bit of discretion here, although I have some sympathy on the points allocation front.

    1. In this debate, I try the most possible not to take account of my preferences.
      I'm a solver who don't like mental arithmetic much, for example mathdoku is one of my least liked variant. But I don't see any reason to put it in the grey area. This is strictly a sudoku. Absolutely fine. I think the fact I put the blackout sudoku in grey area is not a matter of taste.
      The question is: Is it legitimate to say it's a sudoku while it breaks the common rule "each row/column/region must contain each digit exactly once"? I don't have answer, I think both answers yes and no can be ok.
      But the history told us it is dangerous, because it was the starting point for some authors to create everything and anything for sudoku tournament, with weird justifications ("regions are not important, non-repeated set of digits is not important, etc... finally nothing about the basic rules of classic sudoku is important for these authors).
      In the end, I put all puzzles that break some basic sudoku rules (except the geometry, we can transpose sudoku rules in other geometruc figures than squares) into at least grey area.

      It is my strong opinion that sudoku is not everything and anything. I'm still waiting the position of WPF board on this subject. I was asked to be patient. I hope the answer will come in 2017.


    2. Ok, so in the previous comment I described your position as fundamentalist. I think in trying to define sudoku you are both being far too rigid, and at the same time leaving the door open to some kinds of puzzles I'd not like to see in sudoku competitions.

      I think you are completely wrong to dismiss out of hand any variant which doesn't fit into the rigid "exactly once in each row column and region" constraint. For one thing, replacing "exactly once" by "at most once" or "at least once" makes absolutely no difference for a classic 9x9, so why is it that you are sure that the "correct" definition is the one you have chosen?

      It's all well and good to talk about grey areas, but if you want to give me a choice between this blackout, or a classic like "platinum blonde" then the choice for me is obvious. Any definition of sudoku has to take some account of how well the puzzle solves.

      Another factor is it's easy enough to have the classic rules as a base and still end up with things that aren't a grey area but way beyond. I've seen masyu and slitherlink variants that aren't just loop puzzles, but meta loop puzzles where effectively you are placing the clues as well as drawing the grid. And yet the finished grid fits your rigid definition, even though filling in the numbers is basically an after thought once you have got past the puzzle and the meta puzzle.

      On top of this, philosophically why has killer become an accepted variant? On the face of it you might argue non-repeating cages is a part of it but there's a lot of arithmetic and combinatorics that have nothing to do with sudoku and are far more like a puzzle. A puzzle that you might like better, than say, a loop puzzle but fundamentally speaking has just as much in common if you try to relate back simply to rows, columns and regions.

      I don't think you are ever going to be satisfied if you hope for some pure and unambiguous definition. I think you have to be pragmatic and you have to be open to new solving experiences. Novelty for novelties sake is not necessarily something positive but to take completely the opposite position stifles creativity, and is ultimately equally as undesirable in my eyes.

      A fun sudoku is a fun sudoku in my opinion, and we know one when we solve one even if we can't precisely explain what it is that makes it fun

    3. I assume to have a "rigid" or "fundamentalist" position since WSC2015, and I think the only way to fix the issues about non-sudoku puzzles in sudoku competition is to get back or to relate to the foundations that are "rigid" rules of sudoku.
      I try to stay open and still think blackout sudoku (and deficit/surplus) are ok in sudoku competition.
      I know players who are even more rigid than me: "According to me, basic rules of sudoku would have to be valid for all grids in WSC (so that some variants, like Deficit and Surplus, so loved by British creator, would not have any place in WSC)." is a quote of an email I received from a player when I was candidate to be a WPF board member. It shows at least that I'm not the only one to think there is a problem to fix.

      If there is a way to fix the non-sudoku issue without suppressing these kinds of puzzles (blackout, deficit, surplus), I'll be happy, but I'll not be sad if "rigid" rules are applied and if such puzzles like deficit, surplus and blackout disappear from sudoku competition. There are plenty of sudoku competitions that match the "rigid" rules that are fun, contain novelties as well. I disagree to say it's not possible, not desirable, etc..
      I disagree your argument about creativity too: Firstly You have plenty of researchs (see for example here: https://www.forbes.com/sites/groupthink/2013/07/12/creativity-how-constraints-drive-genius/#4971f8f43d89) saying that constraints don't stifle creativity but in the contrary it stimulates it. Secondly we see each year new variants which fit the "rigid" rules and contradict your opinion. I don't think one is more creative by authoring a novelty puzzle that doesn't fit the "rigid" rules than the one who creates a novelty that fits the "rigid" rules.

      I'll separate my answer into several posts, because you brought lot of different things in your post.

    4. "It's all well and good to talk about grey areas, but if you want to give me a choice between this blackout, or a classic like "platinum blonde" then the choice for me is obvious. Any definition of sudoku has to take some account of how well the puzzle solves. "

      I don't agree with you. I think you're mixing 2 different problems here. Any definition of sudoku that doesn't contain "platinum blonde" will not be a good definition of sudoku in my opinion. platinum blonde is a sudoku.
      That being said I never said all sudokus are acceptable in sudoku competitions. I only say it is necessary for a puzzle to be a sudoku to be acceptable (but it is not sufficiant).
      The reason platinum blonde is not acceptable in sudoku tournaments is not because it is not a sudoku, but because it's a too hard sudoku.
      I think we have the same opinion about "guessing sudoku" in sudoku competitions.
      For me the first 2 conditions to accept a puzzle in a sudoku competition are:
      step 0: the puzzle is a sudoku.
      step 1: the puzzle can be solved by logic.
      Both criteria are subject to interpretation and contain grey areas, but if we could already agree with these 2 guidelines, i think 50% of the issues will be fixed (without having "rigid" rules). I have to say honestly that I find it pathetic that the WPF is not able to state these 2 basic principles.

    5. (just a parenthesis: you talked about hybrid between sudoku puzzles and non-sudoku puzzles. Yes I think it's the second part of the problem. A puzzle can fit rigids rules and be a hybrid with loop puzzle for example, it certainly doesn't match to my conception of puzzles acceptable in a sudoku competitions. This is the other axis of the problem that needs some work to be fixed. I spoke about that elsewhere, so I don't want to say more about that now.)

    6. "I think you are completely wrong to dismiss out of hand any variant which doesn't fit into the rigid "exactly once in each row column and region" constraint. For one thing, replacing "exactly once" by "at most once" or "at least once" makes absolutely no difference for a classic 9x9, so why is it that you are sure that the "correct" definition is the one you have chosen?"

      I didn't say I had the correct definition. I said it's a valid question to ask which properties of classic sudoku should be incompressible for all variants.
      The problem for me is not blackout sudoku, the problem is the arguments (or the lack of arguments) you bring to say it's a sudoku. It's a sudoku because you judge it's a sudoku (discussion is then impossible), or "not all properties of classic sudoku are needed", which leaves the door open (a) to all latin squares (a latin square is an irregular sudoku with regions being rows (or columns), latin square is a surplus sudoku with only one region, latin square is a deficit sudoku with N*N single cells regions), (b)to all star battle (we can find a way to formulate rules so that classic sudoku and star battle follow same rules) (c) to puzzles like tic-tac logic that have same properties than sudoku, (d) etc... etc... etc...
      And some people are effectively using this issue to impose non-sudoku in sudoku competitions, using arguments like "if you accept blackout sudoku, then there is no reason not to accept the puzzle X", "there is no rule concerning sudoku, so we didn't break any rules by proposing the puzzle X in sudoku competition", etc...

      In an ideal world, not being "rigid" or "fundamentalist" can work, in lot of national federations it works, but in the competition organized by WPF it is my opinion to say it doesn't work.
      I may be totally wrong, that's why I stopped all activities of creating sudoku, (but why people continue to ask me some sudoku for their competition if my position is so wrong, and why 95% of sudoku competitions actually fit my views if I'm so wrong?)

    7. Fred - just because I don't agree with your (in my opinion) extreme position, does not mean I disagree with all of the points you raise. I am not advocating the opposite extreme position to yours.

      I am simply saying that this search for rigid definitions, rules and order might end up being a fool's errand. Worse, this potential fool's errand might have negative unintended consequences, because as you've agreed there are grey areas and you'll end up "banning" variants based on what can only ever be an arbitrary judgement.

      You yourself say you don't have a problem with blackout sudoku, but then argue that if we can't find the "right" definition of sudoku then there's a chance we should ban this type. To me, that's utterly ridiculous.

      I put it to you that Killer sudoku is a hybrid puzzle. it is a hybrid of Sudoku and Kakuro. It's a matter of taste that the population likes this rather than a hybrid of Sudoku and Masyu.

      Perhaps it's the latin square element that makes Sudoku/Kakuro acceptably compatible, but then what of types like Sudoku/Star Battle, or Sudoku/Battleships, or variants like Shape Sudoku which blur the lines to object placement. You can stretch that logic to then argue that really a loop in a grid (whether drawn or simply implied) is just another placed object. Maybe you or I don't agree with that, but maybe someone else does

    8. The point is that anyone who is forced to draw a line between what is and what isn't sudoku has a very hard job on their hands.

  5. One last point - and perhaps less important - but I feel the way you are arguing isn't very helpful in building a consensus. This problem will be solved by bringing people together, not by driving them apart.

    It's a little hard to be sympathetic with you when you have said that the inclusion of Total Blackout was:

    "only a bad choice"

    Based upon it not strictly adhering to a definition:

    "The question is: Is it legitimate to say it's a sudoku while it breaks the common rule "each row/column/region must contain each digit exactly once"?"

    Which you then back-track on by saying.

    "I didn't say I had the correct definition."

    I can see that you want to have this discussion with someone very much, and the discussion is both legitimate and interesting, but I hardly think you are going to win people round, or even bring them closer together by being so belligerent.

    I fully accept this is probably a case of the pot calling the kettle black, but that's my opinion nevertheless.

  6. Tom, David,

    I'm sorry if I hurt you by saying that proposing total blackout of this difficulty was a bad choice.

    My purpose is not discussion on the subject to find consensus, as I'm de facto not an actor of this discussion in the WPF.
    My purpose is only to understand the people who have different opinions than me. And even if I have no real problem with puzzles like blackout, I'm searching to know the real motivations of authors.
    I find there are a lot of inconsistencies in the answers of a the few people who agree to talk to me on this subject.
    One important question (which is a very minor detail for lot of people, so generally they're embarassed to answer the question) for me now concerning some puzzles encountered in competition: Do you consider theses puzzle are sudoku, or do you consider they are not but it's good to have them in competitions?

    It's hard for me to hear that defining what a puzzle type is
    by its rules is arbitrary. I thought it was the most common way to do it. I would also like to point out what is a big question for me: If you change rules of a puzzle type, it seems to me normally you have another puzzle type (it remember me the puzzle quizz on the blog of Tawan), and I may be wrong but I think sudoku is the only puzzle type which has the property of staying sudoku when you change the basic rules.

    It's hard for me to hear that my position is extreme. It was always the position I imposed to me as an author. In very few cases I created sudoku that don't fit the classic sudoku rules. Once I mixed blackout sudoku with kakuro, but it was not for a competition, it was for the daily league. Then I created once a halved squares sudoku for swiss qualification. It was the easiest variant of the test (5.6% of the total points). And once I created a deficit sudoku for a regional competition. It was an easy one (2.9% of points compared to the total). That's all. I didn't feel more creative with these variants than with others and I think that if I would have had some bad critics of these puzzles "not being purely sudoku", I would have taken these critics very seriously.

    I'm disappointed that discussions that should be primarily on puzzle type very quickly turn into other subjects that are in my opinion not related: creativity, novelty, how fun it is to solve it, etc...

    From my experience, I continue to think it would not be a problem to apply even more extreme position than mine. 90% of sudoku competitions would not be affected in any way.

    I feel the problem is coming from scepticism of some people around the WPF about World Sudoku Championship. They think the fact that organizing a World Championship based only on one puzzle type can't work. So the solution for them is to extend the field of puzzles. How many times I heard that I'm strange to enjoy solving the same puzzle type again and again... Perhaps WSC and WPC is not a competition for the exact same kind of players. Some players might be bored to solve the same type of puzzle again and again. But history shows us there are lot of people who enjoy to solve sudoku again and again, and I'm not happy when I hear from some people that the reason they like it is only because they have not enough "education" in puzzle.

    To conclude, I would like to say that not having answers on this subject that I really don't understand anymore is very hard, and I'm even more distressed to hear from you that you think that giving clear answers would be kind of very negative for competition.


  7. Fred - I suppose I am more interested in having a constructive discussion than I am in indulging your personal curiosity. I am struggling to see whether you are offering anything constructive to this discussion, or whether you are simply interested in criticising authors where (rightly or wrongly) something isn't to your taste.

    However, let me indulge you.

    In my opinion, total blackout sudoku is a sudoku variant. Almost everything that isn't classic sudoku, I would call a sudoku variant. A sudoku variant is not the same thing as sudoku in my opinion. Maybe you can allow minor variations to regions or geometry (irregular, surplus/deficit, tight fit), but really any variation to classic sudoku I have down as a sudoku variant.

    And what is a sudoku variant? Impossible to rigorously define, as I've been trying to say, but the solved grid should at least look like sudoku (with rows/columns and an extra regional constraint). I wouldn't like to go further than that. I would hazard a guess this is what most other people thing, which is why I suspect no one can give an answer to your satisfaction. It really is as simple as that.

    So yes, wacky hybrid puzzles are still sudoku variants. Total blackout is definitely a sudoku variant. The rest - i.e. the solving techniques required to get to the solution - is simply a matter of taste and community preference in my opinion, and this is clearly where we will have to agree to disagree.

    Some grid decorations/constraints/hybrids seem to marry up well with classic sudoku solving, and some are a little more contrived. I've tried to come up with vague classifications of variants in the past but it is very hard - some belong in more than one class, and as we've seen in Slovakia you can describe one variant by another's rules (e.g. Extra region as killer or odd as pencil marks).

    I see your position as extreme because it is clear you see some sudoku variants as sudoku, and some others as not sudoku. Maybe I am the extremist in thinking it isn't possible to draw a satisfying line in the sand, but I haven't seen anyone come close to being able to do so. Perhaps you can enlighten me further into exactly what you think a sudoku is or isn't?

  8. FYI, many puzzle types have variants. I can remember seeing: Tapa, skyscrapers, kakuro, slitherlink, fillomino to name but a few. Sudoku is certainly not unique in this respect; the reason there is a separate sudoku championship reflects its global popularity, even if most of the variants have gone beyond what the rest of the world sees as sudoku.

  9. For curiosity: Do these variants have the same basic rules as the original puzzle or are basic rules also changed?

    1. Yes, I'd say in the vast majority you have the the same "basic rules". I'm not sure they'd really be variants if they didn't.

  10. Ok, I'm ready for constructive discussion, too. The reason this was not my prime intention is that I was trying to have one starting in october 2015, but nobody answered me... All my tries to have constructive discussions failed. That's why perhaps I unconsciously turned my tone to a more belligerent one.
    Not sure this discussion will have an effect outside you and me, but no problem. Also, Thank you for indulge me.

    "And what is a sudoku variant? Impossible to rigorously define, as I've been trying to say, but the solved grid should at least look like sudoku (with rows/columns and an extra regional constraint). I wouldn't like to go further than that. I would hazard a guess this is what most other people thing, which is why I suspect no one can give an answer to your satisfaction. It really is as simple as that. "

    Ok, that's not rigorous, but as I said I'm ok wih basic principle too, as blurred they can be. The 1rst thing that comes to my mind is that, based on your vague principle, to my eyes we can already have doubt concerning some sudoku of WSC2015. A grid that have a digit repeated 4 times surely doesn't look like a sudoku. We could speak about the extra-regional constraint, but can we agree we have a problem with that with the round 4 of sofia? Extra-regional constraint that affects only 40% of cells is definitely a problem to my eyes, and I don't know if you change your mind since 2009 (I know it's long ago), but you have same opinion with second sudoku of the final of WSC2009, which have the same property.
    I'm not sure this is what most people think, because nobody (except some players) answered me clearly "yes, there is problem with some puzzles of WSC2015".
    [I'm sorry to come always with WSC2015, but it's the point where I was really starting to think that I was not doing the same thing]

    "I see your position as extreme because it is clear you see some sudoku variants as sudoku, and some others as not sudoku." Based on which principle? The one you wrote above?
    Yes, you're right. For me, there are some other important things. For example, one another important principle is that the puzzle is about filling symbols (or pieces for manipulative sudoku, of course) into cells.

    Consider this puzzle: http://img15.hostingpics.net/pics/816902filledsudoku.png
    Rules: divide the grid into regions, so that each digit appears exactly once in each region. neighbouring cells that have a bold separation can't be part of the same region.
    (congratulate me to have created a new (fun, perhaps?) puzzle type in 30 minutes)
    The solution is a sudoku solution, but for me the puzzle is not a sudoku, because it's not about filling symbols into cells.
    What is it for you? sudoku? ready to create one for the UK online tournament?

    There are certainly more points that are important to me, I will tell you later if you want.

    What now I cannot understand with your principle, and make me think you may have lot of more tacit criteria when you organize your tournament is, if I should then imagine what should be the kind of tournament based on what you say, I would take for example turkish round of sudoku GP 2013: http://logicmastersindia.com/lmitests/?test=M201306S
    Lot of opinion of players were bad, after this test. I think for lot of players there should be more criteria than the basic principle than the solved grid should look like sudoku.

    1. Fred, your puzzle was more fun than this discussion has become. I'm not the only person you have annoyed by the way, but I'm sure we can put this behind us.

      Most people in Sofia I'm sure would agree those two puzzles weren't a good choice for a championship. Most people are also happy not to let a few bad puzzles ruin their championship experience. I'm not sure what you were expecting - some kind of uprising or revolution? That championship was far from ideal, but you've got to be grateful for all the hard work that goes into these things because ultimately they are run by volunteers. Most people do not seem to have that same level of anger or being upset or whatever it is that makes you keep coming back to Sofia 2015, over and over and over...

      So sure, offer some criticism, but at least be helpful about it. All I see is that you have some definition of sudoku which you aren't quite sure about, and in areas that you aren't sure about you'd rather not run the risk of including these variants in competition.

      Me? Yes, I have some preferences when it comes to organising competitions. I prefer simpler, and more common variants. I tend to shy away from more complicated or novel variants. That's my personal preference, and there is no definition I use, just a feeling. I accept that people will have different judgements and feelings from me, which is precisely why I wouldn't wish to do anything so extreme as to tell them which variant they can and can't use.

      To finish, your puzzle isn't so dissimilar from Tripod Sudoku from that Turkish round. I consider that a sudoku variant just about, but it is certainly not to my personal taste and I would hope not to see too many of these puzzles in sudoku competitions.

    2. Hi all,
      So, I hope normally this will be my last comment here. First, I really want to apologize to all people I could have hurt by my remarks, including things I've written elsewhere, too.

      I would like to thank you, Tom, because that's the first time since I play sudoku that I begin to understand the opposite point of view than mine. I've a conception which is based on classic sudoku rules, so basically a variant for me must follow the rules of sudoku. Since I play sudoku, I always view all things through this prism. This is the ultime reference to me. This is not something I built to arrange things to my preferences. It's really the way I always understood the word "variant". So, for me a sudoku variant is puzzle which has the same rules and properties as say irregular sudoku, but either with different geometry, either with additional constraints. Surely in my conception there is also something like "The solution is defined entirely by the placement of the sudoku symbols". That's not more complicated than that. That's why I already have some problem to qualify puzzles like blackout/surplus/deficit as being "true variants of sudoku". I think I tried to explain my point several times, but perhaps not with good words, because I would never imagine some conception of what is a variant can be so different than mine. Please do not see me as someone not ready to have other solving experience. I'm open to all type of puzzles, I hope you understand I'm only putting some of them in another category than sudoku.
      Then I tried to understand the presence of some puzzles I would not have qualified as sudoku, but I completely misunderstood the intentions. That's where I realize now how my words could have been offensive. I can only say again I'm sorry. I was really thinking someone tried to extend the set of sudoku, or was trying to teach something to sudoku players, or something like that. Sorry for that.

    3. I understand now that the conception of what is a variant of sudoku can be so different than mine! nobody never explained me this way (perhaps it was my fault as I had not the good starting point to understand). And I understand also why from that point of view it's impossible to write definition. I understand that from this point of view all of my complaints concerning some sudoku types looks arbitrary. All of my concerns look like tiny details.
      I still think people who have this conception should try to explain it, even if it's hard, because I'm quite sure I'm not the only one in the puzzle community to have a very different one and to misunderstand totally this way of thinking.
      At the beginning, I really didn't understand your point. By saying "it's impossible to define", I felt it was something even more complicated than what I thought it was, or I thought that it was highly inconsistent, that's why they cannot explain what it is. I think now I get around what is your conception of variant of sudoku. I understand that people who have this conception can feel distressed by how the things turned and how only a tiny part of what they think is sudoku is used in lot of tournaments.

      Now that I understand all these things, I would like to make you know that my goal is not to impose something. Again, I understand how my words may have seemed as wanting to impose my views over your views. It was not, it was really that I didn't get the whole thing, I didn't really imagine someone could have a so different conception. I understand also that your goal is not impose something to me, as I was tempted to believe.
      I don't know what will do the WPF with these opposite conceptions. I'm not sure I would like to take part in all tournaments that contains all aspects of your conception of variant of sudoku. I always have seen tournaments like turkish round of sudoku GP 2013 or David's sudoku surpise on LMI like UFO. I had no explanations other than "I don't understand why they call it sudoku".
      Now I think I understand. Thanks again, Tom.

      I say Sorry again to all of you, it's the end of a very long time of misunderstanding for me.

    4. No need to apologise Fred, I have learned a lot from this discussion too. I am also sorry if at times it got out of hand.

      I think there are still many interesting factors to discuss when it comes to balancing a sudoku competition. I think the Sudoku GP at least makes a start by trying to classify into simple or common variants, and more complex and novel variants. You should have seen over the last 3 years that no competition is dominated by these in the same way that the Turkish round was in 2013.

    5. Wow!! You guys write a lot.

      Just for the record, Sudoku Surprise was designed to be outside the box. It was a gift from me to my friends which I don't think could have been wrapped in any definition. It will not be landing on this earth again any time soon.

      The taxonomy of Sudoku is always going to be difficult. Sudoku vulgaris gives a lot of pleasure to a lot of people. We should never stop appreciating it in its simplest form, and Tom has always been its greatest devotee.

      The various forms and hybrids have their own beauty and make the colourful Sudoku garden a place I enjoy. Fred is right to say that we shouldn't make the Sudoku exotica unrecognisable to the general public. Hopefully, we can tend the garden so that it's somewhere where ordinary people want to visit. Maybe, just maybe, one of your puzzles or one of mine will appeal to a young visitor and a lifelong love of horticulture will be born.

      And, incidentally, I have never been a great fan of double-flowered varieties. So, a further discussion on Sudoku surplus is in order.


  11. Just one more thing for today:

    "the reason there is a separate sudoku championship reflects its global popularity, even if most of the variants have gone beyond what the rest of the world sees as sudoku."

    Is it that good to do things that go far beyond what the rest of the world sees as sudoku? I'm not sure.
    I mean, yes of course we know way more variants than the rest of the world, but when we do things that we cannot relate to what the rest of the world sees as sudoku, this is exactly what I think is bad for us. We start from something which is popular, but gradually we become a closed community doing far different things than billion people solving sudoku.
    I know billion people solving sudoku are not potentially looking to take part to competitions, but I think it's not good to cut the link. That's another reason to make me think the relation to classic sudoku rules is important.

    I'm thinking about that stuffs for a week, so I really need a break now, and make my thinking in order and in english is not easy. I'll continue in a few days if you're interested.



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