The Sudoku Technique We Didn't Know

[@shye229]

thank you so much for covering this puzzle! im very happy to say you found exactly the right trick, this a junior exocet. the 1 in row 5 isnt actually needed to set the technique up but i liked how having it there provided another perhaps simpler way to understand it. the way you described the pattern in the video is the same to how i think about them in general, with these "almost-fish" as it were overlapping in the same cells, from which you can prove there must be at least one of each 2, 3 and 4 in them. i'd be happy to make a video at some point showing how i make classic sudokus, theyre becoming one of my favorite things to set lately, when i get some time. also as an aside, andrews solver isnt the best at exo logic (it cant do senior for example) and it isnt able to see the fish eliminations in the rows, which gives the 234 triple in r7 (which you were definitely right about when you noticed it!) along with some other elims like mirror logic. i dont even know what the second one was doing there, perhaps compatibility testing which is a uniqueness thing. anyway, thanks again for the wonderful solve, this is a puzzle im very proud of so im so happy to see you found the intended path!

[@mirthevanhoorn]

Holy crap. This one totally broke me. Very well done! Thank you for the amazing puzzle.

[@Sujisan4]

That's almost an insanely difficult trick to find.

[@Xoned1]

Shye, as always, Amazing setting. Im glad to see this puzzle solved on CTC and im absolutely amazed with how telegraphed it was that Simon was able to find it live in a solve. And you should definitely go through a setting video on this puzzle.

[@sama477]

Even a short video that just covers exocets would be greatly appreciated!

[@shawnward6607]

"i'd be happy to make a video at some point showing how i make classic sudokus, theyre becoming one of my favorite things to set lately" Please puzzle gods... make this happen... I love classic sudoku... and this is the most elevated classic sudoku i have seen in my short time solving

[@Wecoc1]

26:43 I'll tell you exactly what this is called, Simon! It's called Pure Madness, that's it. Well, if you want to be very technical, it's also a Junior Exocet. Bravo for spotting it!

[@etienneschramm83]

Well, if that's the junior, I don't want to meet papa Exocet...

[@woodchuk1]

Finally found a website that gave a formal definition of an Exocet. Absolutely blew my mind...how would anyone be able to remember all the criteria for how one is composed?

[@woodchuk1]

Can someone, even Wecoc perhaps, give a “condensed” version of Exocet logic, and how to distinguish between that and the “junior” Exocet? At it’s core, is it accurate to say an Exocet in general is similar to a group of overlapping swordfishes, as Simon more or less deduced here?

[@shawnward6607]

May I ask... Simon knows more Sudoku "tricks" then I know of (still learning). How on earth do you know the name and the setting the makes that pattern... within an hour? I just got 3 sword fishes in the puzzle... and gave up,, beyond my brain for a fun puzzle i do in downtime. Cheers

[@Wecoc1]

Look for "JExocet Compendium" on Google and you'll find a very exhaustive post on Junior Exocets. Then there's also Senior Exocets and even madder things like Double Exocets and things like that. On the topic "List of Acronyms" on the same forum I mentioned some more. I don't know about a Papa Exocet but it would probably be even more frightening than a Papa Bear...

[@jelain3917]

May 2020: 4 digits to solve a sudoku? Impossible May 2021: 25 digits to solve a sudoku? Somehow more impossible

[@Playmaker6174]

Extraordinary things only from CTC

[@Varksterable]

In 2022 there will no longer be a grid.

[@itamarolmert3549]

@@Varksterable you laugh, but they have puzzles where you need to draw the large partitions yourself.

[@burrytellam]

@@itamarolmert3549 AKA 'Dots and Boxes'? 😉

[@elizabethgrosvenor153]

I want to see dots and boxes sudoku!

[@Rangsk]

Not only did you explain this technique really well, but you discovered it while live solving! Very impressive!

[@thoughtbyte]

"They see each other through the miracle of madness" Some of the quotes from this channel are just so dang beautiful.

[@anen1987]

27:53

[@bwcbiz]

"The Miracle of Madness" seems like a much more descriptive name than "Junior Exocet". Though if this one is a _junior_ exocet, i don't think I want to see a Senior Exocet.

[@Donrafa189]

It is unbelievable that, without knowing the name of the technique, Simon is still able to use it to solve. From the moment I found this channel, or rather it found me, every episode has been “magic of madness”

[@fduisterwinkel]

"or rather it found me". Haha, great description, that's exactly what happened to me too

[@musicismylove92]

Ah yes, the old classic "Three Overlapping Near-Finned Swordfishes" technique

[@TiaMat99]

Honestly sounds like something you'd find in the kamasutra

[@TimGallant]

@@TiaMat99 Reminds me of Get Smart....

[@smylesg]

That's the second time I've fallen for that this month!

[@madeking4]

34:28 "This is a 2 3 4 Quadrouple" At this point I'm not sure if he just misspoke, or there was another digit in another dimension.

[@NinjaWhaines]

It includes the given 1 with the logic explained earlier.

[@bertbergers9171]

Mark and Simon regularly take groups of cells and randomly announces four or five of them as triples (rather then quadruple or quintuple), but this is the first time of him upscaling a triple into a quadruple ;) (i think). It just means they belong together and you will have to think for yourself how many numbers the group contains.

[@bertbergers9171]

@@NinjaWhaines he didn't mention nor highlight it, so no it doesn't. He was just in talking quadruple mode from the 1234 quadruple in column 3 and 7.

[@jlhidalgo]

I love the fact that shye used 1 as the "pivot number", 2 3 and 4 for the swordfishes (or "the Exocet", if you want), and placed the whole thing in the middle of the grid, so that if you find it, you are pretty sure that that was what you were supposed to find. If it was 3, 8 and 9 in some corner of the grid, even after finding the solution you would be still thinking "maybe I over-complicated things, and there was an easier way..."

[@shye229]

telegraphing is everything! thank you :>

[@d4r4butler74]

@@shye229 Thank You for the Puzzle.

[@CorwynGC]

@@shye229 Once you found the trick, making it 1,2,3,4 and in the center is easy, right?

[@philipnewmansudoku]

To explain for the non-shye audience the (J)Exocet a little better than sudokuwiki does: the Exocet pattern is showing that the base cells must contain the same digits as the target cells. You prove this using the same fish logic Simon demonstrates, and the end result is the same as the quad Simon finds (the four cells in row 5 form a quad, and since the base cells contain the same digits as the target cells you have a quad in the cells Simon found). Sudokuwiki's deductions are limited to the base and target cells, but because of the fish logic you can make more eliminations - the highlighted "almost swordfish" cells in columns 357 (outside of the middle band) are the "cross cells", and in this case we need to fit two each of 234 into those cells somewhere (and since we can only put one in each of rows 139, the cells in row 7 must be a 234 triple). This part is a lot like MSLS/SET - where MSLS/SET can be thought of as a multi-digit extension to non-finned fish, Exocets are akin to multi-digit finned fish. You can also make deductions based on the "mirror cells". In this case, you can think about where the digit in r6c3 goes in box 6. We know it's in one of the base cells, and we know it's *not* in the other target cell, so it must be in r4c89 - so once we put a 6 in r4c9 we immediately know r4c8 is also from 234... and since it sees a 3 in the column, it must be from 24 (and thus r6c3 must also be from 24!). There are additional (sometimes uniqueness based) deductions one can make with exocets, but the above are the most important (and are not uniqueness based).

[@blowitoutyourcunt7675]

Still not dumbed down enough for those who casually enjoy these puzzles! Still too many undefined technical terms, even though your attempt to "dumb" it down was valiant : ) Cheers Ps - Yes I screenshot your comment to look up all these terms later! 3am ain't it though! Cheers!

[@greatwhitenorth762]

Thank you for the explanation, it is appreciated, however you lost me at "the Exocet pattern is showing...."

[@gregorynelson1568]

@@blowitoutyourcunt7675 The Sudoku Solver used in the video actually has links that explain this technique along the right hand column, for this in particular: www.sudokuwiki.org/Exocet Although, this is considered an 'extreme' strategy, so it is going to be difficult and convoluted to follow no matter how it is explained.

[@blowitoutyourcunt7675]

@@gregorynelson1568 Cheers mate!

[@balkthor]

I can't explain it but I get so happy when Simon tells a puzzle "You rotten thing..."

[@Whyamiwatching.01]

Lol, same. I also like it when both Simon and Mark say, “Oh, that’s annoying” with an annoyed tone of voice.

[@kjhg323]

A different way to think about the key logic at about 26:00 is to ask whether more than one of your almost-finned-swordfish can be a true swordfish. The answer is no, because that eliminates two digits of {2,3,4} from the middle row of box 5, which breaks the puzzle. So BOTH of your "fins" must be from {2,3,4}. This also immediately eliminates 1 from r6c3.

[@Kalmakka]

I noticed the same thing as well. It seems like an easier way of progressing once the three-swordfishes-only-sharing-two-fins had been identified, as it doesn't require you to think about the 1s at all. But it seems that you will run into problems later, as it seems that having identified the 1234 triple is the easiest way of eliminating the 4 from r4,5c3. I don't see any other way forward, at least.

[@adamheywood113]

Mark does strike me as the sort of dude who would deliver such devastating news with a smiley face

[@jovi_al]

Learning this technique at the same time as shye was one of the best weeks of my life :)

[@twaddlingalong]

Rules: 3:16 Let’s get cracking 3:25

[@Savukala]

Thanks!

[@twaddlingalong]

@@Savukala welcome!

[@jesperwillems_]

I would LOVE a video going over these more advanced tricks, explaining in detail how they work, how to use them and how to spot them.

[@PuzzleQodec]

Now I understand where that 2250 IQ came from in that collab a few weeks ago. 2000 of that was shye.

[@ragnkja]

That seems a bit harsh on the other 14, but somewhere not too far below 1100 seems plausible.

[@Leyrann]

@@ragnkja PenguinF = Qodec, so it was just a bit of self-deprecating humor. (Qodec is entirely too humble by the way, he barely let me thank him for his contribution to my puzzle when he put almost as much time in it as I did)

[@kr12a2y]

Not enough awe at how Simon discovered and utilized this during a live solve. Rangsk knows.

[@toiryelhsa]

This channel is full of people of such beautiful minds. I am too impatient nowadays to solve sudokus (and even when I was younger I was only doing the simple standard ones), but it is such a treat to follow the logic involved in solving those monsters, and some insights on how they could have been set. I probably wouldn't be able to find the logic myself to save my life, but Simon makes them look so simple. Wonderful, wonderful channel.

[@JohnRandomness105]

22:00 Three broken swordfish, due to two "fins". Suppose neither of the fins were 3 or 4. Then you'd break the puzzle from the swordfish on both 3s and 4s. Therefore, at least one of the fins must be 3 or 4. I don't know what yet to make of it. 23:10 Okay, I bifurcated. (So there.) I tried 23 in the column-7 fin, to pair with 23 in R7C7. 2 quickly broke the puzzle, by forcing 3 into a cell where a 4 had to be. So I tried 3. I kept going, and going, and going... The 3 broke both the 2 and 3 swordfish, forcing the 2 into the other fin. It also resolved the 4 swordfish. The puzzle finally broke (failed) literally in the last two cells, both implacable. (Sigh) So back to the fin, in which I place 46. I'll see if anything can be done. The 2 and 3 are now officially finned swordfish. One will become genuine, while the other may remain finned. (Later) I bifurcated again. 6 broke the puzzle. I've placed the 4. Now I'm stumped. Back to the video. I'll finish the video, but I'm giving up on the puzzle for myself. I seem to have forced a 3 where I had before, and the puzzle broke the same way, except in a different block. 32:20 3 and 2 are in the fins, so they aren't swordfish anymore. 3 is also where I broke the puzzle twice the same way, and I will feel quite vindicated if Simon breaks it that way as well. (Video's end.) Well, he didn't. So much the worse for me.

[@SilverEchoes]

This was fascinating! I'd never heard of an exocet before, and I wondered what the term meant and where it had come from - I supposed it was a sudoku-specific term, but I looked it up in my dictionary just in case. To my surprise, there was a definition: Exocet is a noun meaning "a French-made guided anti-ship missile." The etymology absolutely delighted me: "1970s: from French, literally ‘flying fish’, via Latin from Greek ekōkoitos ‘fish that comes up on the beach’." These overlapping near-finned swordfishes are flying fish!

[@jimbobago]

Sudoku sure does love its fish jargon.

[@sherriann674]

I never thought the day would come when I would be watching someone solve sudoku puzzles on KZbin, yet here I am, utterly hooked. Thanks for teaching me how to do sudoku.

[@squirenonny]

"Even though they don't see each other, they see each other though the miracle of madness" is my new favorite everything.

[@robbutler1947]

Simon, It was good to see that you use sudokuwiki solver. Here is an plain-english explanation of exocet ( from sudokuwiki):"Phil's concise description is impossible to better: When 2 of the 3 cells in a box-line intersection together contain 3 or 4 candidates, then in each of the two boxes in the same band but in different lines, if there are cells with the same 3 or 4 candidates, any others can be removed."

[@Leyrann]

VALTARI! This is going to be a treat. (edited for an explanation of how the technique works, see the read more) EDIT: THIS MAN JUST CASUALLY BUILDS AN EXOCET!!! And yes, you indeed found the exocet, Simon. The exocet uses the same digits that are found in the pencilmarks in r5c46, which means that whichever two digits are in those cells can NOT be in r5c37 in the 'fins'. And therefore, they HAVE to be in r4c7 and r6c3 (though you don't know which way around). And that's the simplest way to then use the exocet once you have recognized it. And indeed, the digits of the exocet (2, 3, 4) can be ruled out of any squares in rows 1, 3, 7 and 9 that are not part of columns 3, 5 and 7 - they work as if they're normal swordfish because you can never put more than one of any digit in the 'fins'. Bonus edit: I'm not going into detail how it worked exactly, but TotallyNormalCat explained on the discord server that his original intention with Wave Particles (which you might remember as that masterpiece Simon solved a week or two ago) was that it would use an exocet, however it ended up not being needed in the eventual solve - it's there, though, if you know where to look! Next morning edit: On the discord server, in the #theory-and-programming channel, Philip Newman and a few others have taken a deep dive into SET for this puzzle. If you're interested in sudoku theory, you'll probably enjoy it.

[@jovi_al]

If I remember correctly, the intention with Wave Particles was not an exocet, but rather exocet inspired. But maybe TNC can correct me.

[@Leyrann]

@@jovi_al Could be, on rereading the conversation it isn't quite clear to me which is correct. Indeed at least exocet inspired.

[@MrHatsuka1]

"They see each other through the miracle of madness". Sudoku and poetry in one beautiful video. Thank you!

[@tyrgannusgaming6657]

I have been able to slog through most classics that Jovi_al, Qinlux, Philip Newman, Sam Cappleman-Lynes, and Shye have made in the past. Shye had to walk me through the utter magic of the exocet technique in this puzzle. Truly a joy to watch it unfold on the channel.

[@XenoSmyth]

“Diabolical grade… don’t know what that means. Probably means it’s hard.” lol

[@ericojonx]

Very very hard

[@thorbjrnhellehaven5766]

In case of "diabolical": I tend to compare difficulty with level of friendships. Diabolical: as easy as the level of friendship with the setter, if it were set by El Diablo, Anything but friend -> anything but easy -> "Probably means it's hard."

[@elizabethgrosvenor153]

Diabolical comes from diablo, which is the Spanish name for devil. Not a jokey, fairy-tale devil like a fiend is, but literally satan himself. Therefore diabolical = worse than fiendish.

[@CorwynGC]

@@elizabethgrosvenor153 Satan is a fairy tale devil.

[@roax206]

@@CorwynGC I believe the point was an original mythological interpretation as opposed to a children's book interpretation. fairy-tale being an interesting term as by many accounts what we know as fairies were derived from some of the darkest myths/folk tales but have been watered down into harmless winged people who go around granting wishes.

[@jimdavis2683]

Consider set equivalence theory on rows 1,3,9 vs. columns 3,5,7. This lets you shovel 2s,3s,4s and no other digits into the remaining free spaces in the columns 3,5,7 (also accounting for the 1 in r5c3 or r5c7). It also allows some logic in the free row 1,3,9 spaces not allowing any more 2s,3s,4s. It also creates a 68 pair in c7r1 and c7r3. This seems like an easier and more elegant path to the solution. Side note: the only reason I was thinking of SET was because I watched shye's video on the subject.

[@ThatGuy-dj3qr]

Thank you, thank you, thank you! It was Classic Sudoku interest that brought me to this channel, and is is primarily classics that keep me coming back. Please feel free to feature more.

[@Poldx]

"Diabolical grade! ... don't know what that means... probably means it's hard" made me lose it completely xD

[@nomore6167]

Since I started watching this channel so many months ago, I've always thought Simon saying "we" was an inclusive thing, to include us in his journey to the solution. Now, I think I'm starting to understand differently. He really says "we" because he has multiple entities in his head, all trying to solve the puzzle at the same time. That explains why he's able to spot such complicated things with apparent ease and solve these puzzles so quickly.

[@MelindaPlainandSimple]

The Shye-Fish Technique. Three shy little fishies hiding in a group. Great puzzle!

[@sotek2784]

A different way to describe the "overlapping near-finned swordfishes" is that *if* two of the 2-3-4 digits were in swordfishes, there would be no way to fill both r5c4 and r5c6 - therefore at most one of them can fail to be in the "fins", therefore the fins are 234.

[@ralvis22]

The "miracle of madness" pretty much sums it up. Sheeeeeeeeesh!! What a ride. I'll be rewatching that a few times.

[@nathandts3401]

A 43 minute classic. I'll just watch this one, I think.

[@Zardox2]

Brilliant solve of a brilliant puzzle! WAY above MY skills, no question! Enjoyed this immensely!

[@DavidNayer]

Absolutely delightful to watch. You continue to provide inspiring lessons in logic. Bravo to Setter and Solver and Learner.

[@amysteele2488]

"...they see each other through the miracle of madness"... love it Simon!

[@amoswittenbergsmusings]

Simon and Mark are already my favourite candidates for the Nobel Prize for Peace but Shye and Simon qualify for distinctions beyond normal. Here's why: I tutor a young lady in mathematics, just because I am completely in love with mathematics. She is considering reading maths in university but is really put off by high school maths. I try to showcase some of the most WOW classical stuff. Of course, I show other people's genius. The other day she asked me what exactly research mathematics is. I referred her to some great videos on YT. If she would have been a sudoku nerd, I could have referred her to tonight's offering. We enjoyed an exhibition of *research* solving, replacing _not a skoobeedoo_ with _hold on a second_ in real time.

[@Varksterable]

Numberphile is a fairly good KZbin channel to see what mathematics can be, rather than how it is taught. But I'm sure you know that already.

[@amoswittenbergsmusings]

@@Varksterable ... and Mathologer, 3Blue1Brown, Stand-up Math and a few others. YT can be a real blessing - and a curse.

[@Varksterable]

@@amoswittenbergsmusings Yes. These things. Mathematics is a beautiful thing that so few people see for what it actually is. "Doing bigger sums" is _not_ what mathematics is about. It is about exploring the universe. Understanding how the world fits together and how we can model it, understand it, change it. It is about how we live, how life works, how life even exists. All science is based on mathematics, and it is fundamental to all braches of it. Without mathematics, human knowledge would be nothing. And also, if you add the digits 1 to 9 you get.... 47! 45. Oops

[@corsiKa]

Simon: Here's some data we have on twos and threes, but I'm not going to use this knowledge. Also Simon: We don't know much about twos. Also also Simon: Look what we could do if we were to use that knowledge tho... Beautiful, simply beautiful.

[@vk7021]

Start of video: “Normal” sudoku rules apply End of video: Three overlapping near finned swordfishes is a miracle of madness :D

[@jimbobago]

The rules may be normal, figuring out how to use them show how abnormal (and I mean that in the most respectful way possible) Simon is. I need to watch this at least one more time just to really absorb what is done here.

[@hbmason3]

I’d love to see a constructor’s video on this puzzle

[@parrotraiser6541]

I had no idea that the puzzle has generated such an extraordinary jargon.

[@samus88]

I have yet to spot a swordfish, finned or regular, on a classic sudoku on my own, let alone an "exocet", whatever that word means. Fascinating stuff

[@sailmichigan8225]

Me too. I can solve most Sudoku using the Excel program I wrote. Sometimes I have to resort to a SWAG (scientific wild ass guess) which opens the flood gates. But this puzzle requires multiple good guesses. Difficult; like hitting a dozen 3 pointers in a row. My program recommends solution values about 95% of the time. For the remainder my goal is to present the data in a format that enables me to spot an exclusion opportunity. I am looking for presentation method to make solving easier, not necessarily automatic. I googled Exocet. First step is to learn the terms: Base cells, Target cells, Companion cells, Mirror cells, Cross-line cells, Escape cells. Once terms are mastered there are a dozen rules governing relationships between cells. Learning stuff on KZbin is often difficult. The authors get paid to drag things out…providing easily understood information is not the agenda. In this case; 42 minutes of blah blah blah and only 2 minutes of relevant information. This is the first time I have looked at the comments in any detail. Interesting there are many people working hard on sudoku. I hope there are people working half as hard on problems like preventing wars, avoiding covid, stop global warming….

[@rustybarrel516]

I think it means he cast out a demon. A miracle indeed.

[@samus88]

@@sailmichigan8225 What in the actual hell? Get out.

[@KallePihlajasaari]

@@sailmichigan8225 Everything you say is spot on. The last part is the most germane. I have spent the better part of 15 months of free time trying to advice people that there is a natural prophylactic for most winter season ailments and nothing seems to stick. So sometimes even I stumble on arcane sudoku lore that blows my mind. investigate vdmeta at the usual domain and let me know what you think and share the information is you can.

[@kitsapview7024]

Hey Simon, A while back you had a brief video that mentioned "the worlds most difficult classic sudoku" which you said people some times try and throw in your face "Oh yeah try and solve this!" And you did talk about solving and the future ways are minds might go to solve these puzzles. And look now. Tatooine Sunset and now this puzzle and the many more sure to come. This is a great channel, solving puzzles of all types but also experiencing the joy of those puzzles. My girl friend is enamored with me for being a sudoku nerd!

[@danielwow3700]

"they see eachother through the miracle of madness" - 27:47

[@luisfelipetrigo]

thanks for sharing. At 39:12 a three is assigned for r8c9, which makes threes at r4c7, r6c2, r1c3, r2c4 and r7c5... which completes all threes. From that point on all other digits fall by sudoku.

[@Marsaw]

So the way I saw it was as soon as you showed the overlapping 2 and 4 double finned swordfishes, I imagined both of the fins being confirmed as not 2s and not 4s, and I realized that would break the cells in row 5, box 5 by making them both 3. That meant you needed at least 1 of the fins to break a swordfish because they were mutually exclusive. Then when you found a two-finned swordfish on 3s that had the same fins and saw those same cells in box 5, I realized that now you needed at least two of the swordfishes to break, which meant both fins had to have some value that broke a fish and that they would have to be different. Thus, R4C7 and R6C3 had to be either 2, 3, or 4, which would give up the 6 in box 6. That seems to be what the first solver did.

[@RPWhitworth]

I plugged this puzzle into the Good Sudoku app, and it told me "Our solver couldn't complete this puzzle" 😂

[@gordonclark7632]

I started watching these videos thinking I might try and practice being logical. After the names and moves, I am totally confused and realised I am not logical.

[@drstkova]

My shout-at-the-iPad moment came today at 33:02 when Simon mentioned 3s and then didn’t place the 3 in box 4, which unwinds a load of stuff. :) My “I totally didn’t follow that” moment was earlier, when he figured out the 1234 quadruple…

[@sama477]

27:53 "They see each other through the miracle of madness!" The only thing missing at that point was the mad scientist laugh as Simon's hair looked appropriately messy already.

[@CannyK9]

I'm an amateur, and solved this in 78 minutes with a technique I've never used without bifurcation, so feeling very pleased I was waiting for the moment it was used in the video and it never was! I've now read about exocets and Bowmans and I don't think it's either, so can anyone tell me what this is? I coloured the different 4s in box 3 and 7, and traced their respective colours through the grid to determine that they affected each other and could only have two options, which ruled out fours elsewhere and placed some digits. This allowed me to do the same with 3s, which overlapped mind-bendingly with the 4s to lock 3 and 4 into several cells, which eventually allowed them to be disambiguated, then doing the same with the 8s finished the puzzle. Loved the video as always, but seeing a different solution feels like I've been invisibly robbed, like someone has accidentally taken my shoes and left their near-identical ones~!

[@nebuzaradan7022]

Also an amateur but came here to comment that I think I did something similar -- (after placing the two 5s) colored the possible 8s in box 9 and followed them around the whole grid, which interacted with the 4s and allowed me to place four 8s and two 4s, then did something similar with 1s and 9s which again interacted with the 4s.

[@Swisswavey]

I think the technique you used is called bifurcation

[@cliffthecrafter]

I think the exocet that the software showed is what I spotted watching the video after you marked the three swordfishes but before you spotted the quadruple. Basically, if there is no 2 in either F3 or D7, there is a swordfish on 2s that prevents 2 from appearing in E4 or E6, and the same thing applies to 3s and 4s in those cells, and as a result, since E4 and E6 were already limited to the digits 2,3,4, F3 and D7 have to contain two of the digits 2,3,4 to avoid removing too many options from E4 and E6. And looking back, F3 and D7 actually have to contain the same two digits as E4 and E6.

[@Exkajer]

Those "swordfish breaking cells" needed to be filled with nearly-swordfished digits. From pencil marks in R5C4 and R5C6 you can see that only one of the nearly-sworfishes on 2/3/4 is actually a swordfish while the other two take R6C3 and R4C7. This is how I see it. And it is possible to spot before the quadruple thing, just after you shown swordfishes.

[@MartsGarage]

I didn't even try this one, way above my skill level. It even broke a solver I downloaded too. So well done Simon. Love the classics. Mart in Solihull.

[@philipnewmansudoku]

The Classic Sudokult is open to all who seek enlightenment...

[@Leyrann]

Join us. We have sue de coqs.

[@tyrgannusgaming6657]

Very exociting!

[@StefanPettersson]

An amazing solve! Very impressive!

[@ellaenchanted2399]

When a classic has a similar length on the channel as some of the 'easier' devil puzzles, you know it's time to hide. At this point, I'm waiting for 2022 when any vid below 30 will be considered amateur hour lol :P

[@lydia7649]

I would love to see a video of shye setting this

[@Paolo_De_Leva]

Magnificent solve. Crystal clear explanation of this *junior exocet* trick. I am glad this puzzle was included in volume 2 of *CTC Greatest Hits.* I enjoyed watching this video 3 years ago and enjoyed watching it again now.

[@danclements2071]

You should call this technique a Stained Glass Window

[@milkom2021]

One of the best videos on the channel! You can almost see the cogwheels spinning 🤔⚙⚙

[@chrisg6597]

Maybe the pattern should be called a Quantum Quadruple because the digits aren't connected yet are linked or effect each other.

[@stephencolwill148]

Perhaps even "entangled quadruple" - also from quantum mechanics.

[@pritikshettry2261]

Simon, I'm always amazed how you are able to solve the most difficult puzzles. Kindly share which software you use to solve these. So many colours. Please let me know. Thanks.

[@christermagnusson6463]

Valtari (stress on the first a) is an Icelandic word and a song by Sigur Rós. It means (steam) roller, a machine used to make even an uneven surface. Not a good thing to be subjected to but Simon managed to get out of it.

[@bertbergers9171]

Congrats Simon! Greaatttt find! What a thing. Is exocet named after the rocket? Because this technique will blow multiple brains in one huge bang anywhere!!!

[@jessicaschirle5974]

Would've been perfect to release this solve on May 23. There's a great Sigur Rós album called Valtari that was released on that day 🙂

[@mattipaajanen4109]

I really much enjoy your channel, and watching the solves! Truly remarkable puzzle! The title of this puzzle "Valtari" though, I never realized it has a meaning in English. It is a legit Finnish surname, statistics pulled that there have ever been 410 ppl with that surname in Finland (but we're a small nation). The other spelling, Waltari (as native Finnish doesn't distinguish between the two, and spelling has changed over time), is a bit more rare, but one of the most famous Finnish novel author outside of Finland was Mika Waltari.

[@HugSeal42]

This technique needs to be Called a School, it's a bunch of fishes that teaches you something :)

[@morosleviwalker61]

That’s so cute and I’m very upset no one has told you this yet >:(

[@ericpraline1302]

"Please don't bifurcate" - easy for you to say. Very occasionally I can spot an X-wing but that is about my limit when it comes to classics.

[@jfirth816]

13:30 both faux finned swordfish and red herring. Time for a seaside holiday perhaps?

[@toadfrommariokart64]

30:40 "that square has become a 2 by sudoku" applying sudoku logic in a classic sudoku? madness

[@evajanin2970]

37:08 Computer: "Diabolical grade" Simon: "Don't know what that means, probably means it's hard?"

[@Neodragoon3]

Could we do something with the fact that all the 4s marked in green (in your overlapping swordfish patterns) are actually located on Phistomefel's inner ring whereas the corners could only receive two more 4s ?

[@simonplanting5948]

I made this rod, for my own back.... classic... great... thanks Simon for enjoying this on so many levels..

[@deathray3004]

36:29 that 3 is resolved since the rambling began at 30:50. that's the real madness.

[@Coyotek4]

48:54 ... I'll admit, I just didn't have the patience to solve this one the way I was 'supposed' to. I ended up bifurcating ... a LOT ... in order to get to the end. Now I can watch the video and see the wonderful technique that completely eluded me. EDIT - that technique was something else, all right!

[@MadScientist212]

I never would have had a chance of solving this or finding the technique without watching the video, but I was pleased that while watching the video I actually did spot the technique shortly before Simon explained it. Once he drew the three possible swordfishes and fins, I paused the video and had a think. The way I came to it was to first realize that there couldn't be both a 3 swordfish AND a 4 swordfish because of the 34 in r5c6: both digits would be ruled out. This was all I got at first and I nearly hit play but then I thought about the 234 in r5c4. And so I realized there also couldn't be both a 2 swordfish and a 4 swordfish either, because then both r5c4 and r5c6 would have to be 3. Ditto for why there couldn't be a 2 swordfish and a 3 swordfish, we'd have two 4s in row 5 then. So of the three hypothetical swordfishes, only one can actually exist in the grid without breaking the puzzle. And for it to be possible for there to be only one swordfish, both of the "fins" have to be occupied by a 2, 3, or 4, and they have to be different digits too, or else again we get multiple swordfishes and break the puzzle. EDIT: And then following up this, once both fins are occupied, there naturally has to be a swordfish with whatever digit among 2, 3, and 4 we didn't use in a fin. From reading the comments it sounds like this pattern alone is apparently the "exocet," and it is enough to place the 6 in box 6, but the fact that there are only two possible places for 1 in row 5 gives us further info and the weird 1234 quadruple in box 4 and 6. A really interesting and nifty technique. And also really good instincts and solving by Simon to hone in on this so quickly despite not even having heard of the technique before. Like I said at the start, without the video I would have had no hope of finding anything useful. I probably would have gotten some corner marks and most of the 5s and then been completely stuck.

[@jdtsmith]

Your logic made really intuitive sense, and is what the first exoset solver in the computer solution does for you (places a 234 in box 6, netting a 6). But, as I discovered the hard way, it is not enough. Once the off-fish fins are populated with 2 differing digits (2,3,4), you may notice 1's can only be in two places in row 5: on the only 2 cells in the overlapping swordfishes! Since each row of a swordfish needs one member of its value, whatever digit is the "odd-man out" from the fins must be on Row 5 in those fish-overlap cells. And since 1 can only appear in either of these two on row 5, the other overlap cell on row 5 must therefore be a 1. So THIS is how you prove it is a 1,2,3,4 quadruple, which is absolutely required to make progress. The computer solver later concocts ANOTHER Exocet on these cells and a bunch more chicanery to come up with a solution.

[@Sertifi]

Hello CTC. Would you perhaps like to numerize your Sudoku challenges so if you ever return to them (or giving the possibility to) you could refer to them with a number? I'm more than interested in hearing more in-depth analyzation of this challenge. Appreciate the calm and enthusiastic demeanor to each and every puzzle you publish.

[@l3igl2eaper]

"I make this rod for my own back." I like that.

[@mindassassin]

Mom: What are you watching? Me: Sudoku. Mom: Why is he talking about fish? Me: ...reasons...

[@MrRyanroberson1]

22:32 forgive me if i'm wrong, but by having a triple swordfish, isn't it guaranteed that those two dud cells (the ones that ruin the swordfish) have to contain a two, three, or four because if they contained anything else then you would have to fit three values in the two cells in row 5?

[@asphias]

There's some more beautiful logic in the puzzle that Simon didn't catch: the fours in box 3 and 7 communicate through the fours in box 2 and 8.(which are restricted due to the limited places you can place four in row 2,8 and column 5). This overlaps with the 3s on row 2 and 8, which means that if the 4 is on R2C8, it forces a 3 in R8C9, and a 34 pair in the right wing of the exocet. similarly, if the 4 is instead on R8C2, it forces the 3 into R2C2, and a 34 pair into the left wing of the exocet. Finally, after eliminating 1 from R2C8(which uses the fact that if 1 is not in R5C7 it must be in R5C3, and forces the 34 pair to the right wing of the exocet), you can use that 1 can only go into R2C1 or R2C9, and 2 can only go in R8C1 and R8C8, to prove that when the 34 pair goes in the left wing of the exocet, 12 are forced into the right wing, and vice versa. I do think directly solving for the exocet is much more extravagant, but i really did like the way the communicating fours and threes interacted into forcing a 34 pair on one side of the exocet.

[@Thedudeman8282]

I recently bought your killer sudoku app and it is awesome. Thank you for that.

[@MichaelJPartyka]

Amazing how that one insight is everything needed to unlock the puzzle.

[@TheBiggreenpig]

Wow, I didn't expect there is anything that could beat fpuzzles in vanilla setting.

[@tyrgannusgaming6657]

Oh, you would indeed be surprised. There's 4 or 5 techniques it can't see

[@Aoderic]

Valtari is indeed Icelandic 🇮🇸 for steamroller 😊

[@matthewgraham2619]

I don't understand the rules...

[@Tombsar]

They feel... incomplete, somehow.

[@elizabethgrosvenor153]

I don't know what the digits 1-9 add up to!

[@compdude551]

Lol

[@redcreeper2024]

@@elizabethgrosvenor153 45

[@stevesebzda570]

@27:46 : Those 4s not being in there (in col3 of box4) due to the strange cool 1234 quadruple. That puts the 4s in col2 there (that's going to place the 4 down in box7 - which is going to place the 4 in box8 - which is then going to shoot right up and fix that 3,4 in box5). Now, back down to row8; There's now a 289 triple fixing that 3,9 over in box9. Super cool puzzle. [Not meant for paper solve, I can tell ya that lol ] Super cool how it unwound in different ways from there. Excellent job Constructing. :) 😄

[@johnpedersen3458]

Got it. Took about 15 min. Not sure if I used the same technique, but will watch now. Good puzzle!

[@TwoandaHater]

"Miracle of Madness" would've been a great title for this one.

[@martinepstein9826]

Here's the way I see it. We have these four key cells: r5c3, r6c3, r4c7, and r5c7. We know 1 is in a key cell by ordinary sudoku. For x = 2,3 and 4 we can say "If there is a swordfish then x is in a key cell. If there is no swordfish then x is in a key cell". So 2,3, and 4 must also be in key cells.

[@mikepictor]

"They see each other through the miracle of madness" - Right...well I'll just try and work that into my solving toolset

[@DubioserKerl]

"Through the miracle of madness" sounds like a badass prog metal album name!

[@michele8208]

Thank you from a novice..yr explanations are great.

[@Keythong]

"I'm afraid this is all complete gibberish, I'm sorry" that's exactly what I was thinking too.

[@patriciaodegard1231]

It appears that, while the "almost locked set" is a thing, the "almost finned fish" is also a thing. Amazing how SImon zeroed right into it.

[@ridefast0]

Above my pay grade, can't imagine me spotting one of these in the wild. Congratulations to the setter and to those who can solve it!

[@BozoTheBear]

I'm in awe of both setter and solver!