Could You Help Me?

** TODAY'S PUZZLE **
A very original and interesting sudoku today from SSG called Covert Confinement. It mixes up Sudoku, Nurikabe, X-Sums and Killer rules and we love it! And you might be able to help Simon spot what he thinks he's missed at the end of the solve.... :)
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Rules:
Normal sudoku rules apply. Shade some cells in the grid such that all shaded cells form a single orthogonally-connected region and no 2x2 square is fully shaded. Each unshaded region must contain exactly one clue cell. Each unshaded region is an “X-killer cage”. Digits within a cage may not repeat and must sum to the total given in the corner of the clue cell. Additionally, the digit placed in the clue cell must equal the number of cells in the cage. The cell with a grey circle must contain an odd digit.
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[@SSGranor]

Thank you so much for a lovely solve of my puzzle! You followed my intended path through it quite closely, including the intricate bit in the top left. (It's possible to look at that in a slightly more holistic way; but, it all amounts to the same thing.) And, I'll admit to giggling a bit about the sting in the tail in the middle rows. There are a few ways of seeing it; but, it really is all about the 9s. As for the puzzle's title, it's a play both on the nature of the puzzle (i.e. hidden cages) and the origin of the term "nurikabe," which, to my very American understanding, is, in Japanese folklore, a type of spirit that manifests as an invisible wall. Much like Simon, I would love to see more puzzles like this. The interaction of the cage logic and the nurikabe logic just felt so natural to me (including the use of the X-killer rule to turn cage clues into standard nurikabe clues). And, I do know of at least one other puzzle that works this way - udukos' Nurikabe Killer Sudoku, which you featured on the channel back at the beginning of 2021. I suspect there's a lot more that can be done with this idea than can be contained in just two puzzle, though.

[@azrobbins01]

Thanks for sharing your puzzle with us!

[@TheFreeBro]

I love this combination of Nurikabe and sudoku. I agree with Simon that a series of these would be nice. If not a genre

[@glum_hippo]

I think just one more judiciously placed grey circle might have proven more satisfactory at the conclusion - but that's highly subjective and you'd probably end up getting people complaining about that as well. Nice puzzle!

[@SSGranor]

@@glum_hippo I chose that location specifically _because_ it ultimately only eliminates a single candidate. That way it doesn't really interfere with the nurikabe/killer logic. (Although, it was pointed out to me at one point that it actually does introduce a uniqueness argument for the size of the 29 cage.)

[@not-on-pizza]

Speaking of uniqueness, you _can_ just use BUG to just put a 9 in r4c6, but I can understand some people really not wanting to do that...

[@MyriamTT]

Its amazing how Simon's aversion to do Sudoku in a Sudoku puzzle makes every puzzle much more difficult.

[@toxicara]

He does that every time 🤣

[@christinegermundson4286]

I'm so glad I found CTC! I've been writing my master's thesis this spring and the CTC videos have helped me to relax and wind down in the evenings, after a stressful day. Now I'm one week away from the deadline and looking forward to every CTC video this last week of university!

[@inspiringsand123]

Rules: 03:41 Let's Get Cracking: 07:24 Simon's time: 53m14s Puzzle Solved: 1:00:38 What about this video's Top Tier Simarkisms?! The Secret: 4x (09:09, 09:11, 09:18, 11:22) Bobbins: 1x (17:12) Maverick: 1x (37:54) And how about this video's Simarkisms?! Ah: 12x (12:30, 12:37, 14:53, 15:17, 17:25, 30:40, 33:56, 39:57, 39:57, 43:25, 43:25, 54:55) By Sudoku: 11x (19:53, 26:19, 35:53, 35:57, 40:28, 47:48, 48:39, 51:50, 51:57, 52:27, 55:37) Wow: 10x (13:25, 27:26, 28:32, 30:49, 31:55, 33:09, 40:37, 42:42, 47:46, 58:54) Hang On: 8x (25:26, 29:25, 34:03, 34:03, 34:03, 38:23, 41:48, 46:49) Pencil Mark/mark: 6x (05:45, 39:26, 39:44, 43:02, 45:48, 55:43) Lovely: 5x (17:49, 18:57, 30:13, 49:42, 1:01:33) Good Grief: 4x (18:40, 30:49, 35:04, 47:51) Sorry: 4x (12:23, 22:39, 44:48, 57:50) The Answer is: 3x (15:23, 38:30, 43:39) Beautiful: 3x (00:29, 19:15, 54:46) Nature: 3x (17:29, 20:03, 53:27) Goodness: 2x (52:52, 1:00:39) Naked Single: 2x (26:25, 26:46) Stuck: 2x (17:08, 22:51) Brilliant: 2x (1:00:44, 1:00:46) Shouting: 2x (00:53, 01:24) Obviously: 2x (02:49, 15:25) What Does This Mean?: 2x (27:27, 32:31) That's Huge: 2x (18:49, 42:48) What on Earth: 1x (57:43) Diddly Squat: 1x (43:00) Useless: 1x (36:02) Recalcitrant: 1x (11:19) Missing Something: 1x (23:44) Horrible Feeling: 1x (22:49) Incredible: 1x (03:03) Elegant: 1x (48:24) Deadly Pattern: 1x (57:15) Gorgeous: 1x (18:40) Epiphany: 1x (40:21) Checkerboard: 1x (08:29) Puzzling: 1x (07:11) In Fact: 1x (37:51) Whoopsie: 1x (10:21) Fabulous: 1x (56:26) Have a Think: 1x (54:05) Cake!: 1x (02:12) Most popular number(>9), digit and colour this video: Twenty Nine (10 mentions) Two (95 mentions) Green (56 mentions) Antithesis Battles: High (3) - Low (2) Even (9) - Odd (3) Unshaded (11) - Shaded (2) Column (15) - Row (5) FAQ: Q1: You missed something! A1: That could very well be the case! Human speech can be hard to understand for computers like me! Point out the ones that I missed and maybe I'll learn! Q2: Can you do this for another channel? A2: I've been thinking about that and wrote some code to make that possible. Let me know which channel you think would be a good fit!

[@956675]

Maybe add in "avoid the 2x2"?

[@antoniovazquez8644]

Accidentally miscounted the “ah”’s, you doubled the one at 39:57

[@boudewijnj.m.kegels5198]

@@antoniovazquez8644 43:25 as well

[@pouletbelette]

Why am I so excited about Simon and Mark meeting with Qodec?! I'm so pleased!

[@KevFrost]

To paraphrase Arthur Dent: "this must be a new definition of the word simple that I was previously unaware of"

[@martinbull-gundersen8878]

A little late to the ball, but watched this after solving it to see how Simon coped with the end. There is a "trick" I remembered reading a long time ago to solve such patterns: count the digits. Since there are ONLY pairs and one single triple, only ONE of the digits will appear an odd number of times in the pencil marks. That digit has to go into the triple. I came to see if Simon did explain why, because I've kind of understand it, but can't explain it very well. Very nice puzzle anyway, and nice solve :-)

[@KombatGod]

I love these kind of region-coloring puzzles! I want to share a pencil marking convention I made up that I found particularly useful: in cases like at 13:05 where a cell could include a specific digit if it's in the region but you don't know if it is (and corner marks are not useful) you can write a 0 to mean that the options are incomplete and the ones you wrote are only valid if the cell is in the region. For example in that case I put "03" in all four cells around the 2, meaning that each of those cells can either be a 3 if they're in the region or something else if they're not. Or around the "6" cages I wrote 0124, because those were the only options for a cell in the region. That may sound confusing or useless but I find myself doing it in almost every puzzle like this, where you have to calculate possible sums of differing lengths (which may be sandwiches or x-sums for example) Of course the 0 can be replaced with all the possible digits at any time, but if at one point you find that you remove a pencil mark and you're left with a 0 in the cell, that tells you that the cell can't be in the region any more. I'm actually not sure if I invented anything but I thought I'd share it because I was surprised by how well it works.

[@BedWords_]

i like this, i found myself wanting to notate that somehow in this puzzle and that seems like a good way to do it (until you encounter a 0-8 sudoku :P)

[@reganmartin4126]

The stumper at the end is what I seem to get on most puzzles! Thanks for showing me the way out! I usually start guessing, and that gets me into chaos!

[@georgelane6350]

I've been guessing for months, but this is the first time I actually saw it. I think once you've seen a few you know the pattern you are looking for and you can pick the 'weak' cells to test first

[@martinbull-gundersen8878]

There's actually a very easy trick to solve the part at the end. If you notice all you are left with is pairs and one triple, you can count the digits. You will notice that the only digit that is pencil marked in an odd number of places is the 9 (all the other digits is pencil marked in an even number of places). That means that the triple HAS to be a 9. Don't ask me why - I just remembered reading that a long time ago - and although I can't explain it, I can kind of see why it has to be :-)

[@topilinkala1594]

@@martinbull-gundersen8878 It's called BUG. And you just told how to solve one. It's nice to see a BUG because it's so rare and I think Simon even knows what one is. Why didn't he regonice it is a mystery to me. I think they should have a showcase of a classic sudoku ending in a BUG to demonstrate how it is solved.

[@nemuchan]

Wow, need a picture of you 2 + Codec tomorrow !

[@s.grey.k]

1:43 hello from Atlanta! Quite a surprised and pleased to hear a shout out to my home state. Love the channel, especially the really long videos when I'm stuck inside all day. Much love from Georgia

[@chrisbattey]

For the tangle at the end, there's a shorthand I use to recognize the kind of chain of possibilities you get from bouncing around between pairs of two-valued cells that are the only two possibilities for both values in their row/column/box. It basically represents the same logic as what Simon does but wrapped up in a simple rule so you don't have to step through the options each time. Suppose you have an 1/2 pair in two cells X and Y - i.e. X and Y share a row, column, or box, but not all three of those dimensions. You're looking for the following situation: a) X sees another cell Z with two remaining options, and X and Z are the only possible locations for 1 in a dimension they share, and b) Y sees another cell W with two remaining options, and Y and W are the only possible locations for 2 in a dimension they share. Then you know that Z is 1 if and only if W is 2 - in particular, their other options go together or not at all. This is useful when those other options are both the same number, or if they're both seeing the same cell that only has those two options. In my case, I started with the 1/7 pair in box 6 - r4c7 and r6c7. r4c7 and r4c3 (which is 7/9) are the only 7s in their row, and r6c7 and r6c6 (which is 1/9) are the only 1s in their row. Since the other values besides the 1/7 pair we started with are both 9s, we know that either both those square are 9s or neither are, and we can see that "both 9s" causes a problem with row 5. Simon essentially applies the same technique starting with the 6/8 pair in box 4 - 8 in row 4 can only be in the 6/8 or the 8/9 (r4c8), and 6 in row 5 can only be in the 6/8 or the 6/9 (r5c6), so either both the 8/9 and the 6/9 are nines, or neither is - and "both are 9s" causes a problem with row 6.

[@ecMathGeek]

Thank you so much for this. It makes a lot more sense now that I can see a clear logical pattern. I ended up just guessing on my own solve (and felt very frustrated that I had to use that approach).

[@mute1085]

This was a very lovely puzzle, approachable even for me. Seeing the video time I wasn't sure if I should try it today, but it went surprisingly well. A lot of small steps to get to the end, but never getting stuck staring at an empty grid for fifteen minutes. I resolved the final pattern by observing how 68 pairs in r45c2 interact with 89 in r4c8 and 78 in r5c4, ensuring that in 79 pairs in r45c3 top digit is 7 and bottom is 9 no matter which way 68 pairs are placed. Not sure if there is a name for that technique.

[@emilywilliams3237]

I really loved watching you do this - especially the Nurikabe part, and also the logic in column 1 around the 12 and 10 cages. This is the kind of thing that I have seen you (or Mark) figure out many times, and understood at the time, but could not apply myself. BUT I think that I am getting it now, more internalized, and I think I could apply it. Thanks so much for this puzzle, SSG, and for including it in the channel, Simon. Oh, and I love the word "nonplussed" - today's cool vocabulary word. I laughed out loud at your pointing out that a particular bit of logic, while true, would "still be a very boring conversation at a dinner party" - I am heading to a dinner party this very evening, so how about I give that a try and see how I get on?! 🤣 Thank you so much for the varied types of entertainment and inspiration this channel offers - love it.

[@dathandijksma8882]

I cannot do any of these. I struggle with medium difficulty on my phone. Love the vids. go on and make my jaw drop at the logic.

[@waynerohrbaugh8059]

Awesome go as always Simon. Thank you so much, Aaron was in awe that his name got called out when we watched tonight. It was the icing on the end of his day! Thanks again.

[@th.nd.r]

Beautiful setting and solving, so many good moments, and lots of potential in this sudoku-nurikabe combo!!

[@eduardogamboa9387]

This has easily been one of my favorites so far, hope there are similar puzzles to this one in the future. There is something about this that its just so enjoyable to watch

[@killamoosdraree730]

Around 26:00 it is forced by some sort of weird arithmetic. I sat and crunched the numbers eliminating digits that would not work (arithmetic is weird for sure). The simple sudoku at the end also caused me to sit and crunch numbers... luckily I focused on the only box with 3 digits (r4 c6) and thought about how there were only 4 possible locations for one of those digits. So I tried that digit in r4 c6 and eliminated it as a possibility which gave me r6 c6 unlocking the rest. I am not sure if there is a nickname for that sudoku logic, but it has worked for me in the past on other puzzles. It still took me nearly twice as long to solve this as the length of this video. I always find these puzzles to be very enjoyable. Thanks!

[@ekscorels4286]

Amazing! Hope to see more of these types of Sudokus!

[@dwagyn2202]

I love watching these! They're so calming and seeing the way you work through the logic is fascinating, I feel like I'm learning a lot! Thank you!

[@NiennaNeryam]

In the end, r6c7&8 have two options: 1,8 or 7,9. 1,8 would put 7,9 in r4c7&8, which leaves r3c3 with no options.

[@MrCheminee]

I can't help but being so impressed by how quick you solve these things. Got stuck on this one for a while, took me almost 6 hours all together. And still I see you just taking your time to explain certain things I just took for granted.

[@elfdogre2181]

"The 1 & 7 are done by the 1 there" - poor 7, sitting in r8c1 for a while being ignored...😜

[@BedWords_]

lol i'd been pointing at that 7 as well like a kid watching blues clues

[@steve67339]

Really enjoyable content, as usual, keep up the great work. It might be too much work, since you release so many videos, but in a recent video you mentioned that you always try to stay beginner friendly (much appreciated), but I have a suggestion how to improve that while simultaneously dialling back on the (for more experienced viewers probably redundant) explanations. You could show an explanation of term in the corner with the rules. The rules corner isn't used that much, after you went over it in the beginning (and would still be there most of the time anyways). E.g. you mentioned skyscraper logic. When you mention it, show an explanation/definition of it for maybe 20 seconds and then return to the rules. Whoever is familiar with that term can continue watching and people who aren't can see it on screen (and pause if necessary). Obviously by no means necessary, because people can pause and google the term in question, but probably an enhancement none the less. Doesn't mean you can't explain it in the recording, especially if it is more complex, but for simpler terms that could be useful.

[@longwaytotipperary]

Happy birthday Aaron! Thank you Simon for saying nice things about our state (Georgia)! It seems strange that someone so far away would even know we're here. But you have traveled extensively and most people will eventually go through Hartsfield-Jackson Airport either intentionally or on the way to somewhere else. 😉 Enjoyed the puzzle and your enthusiasm!

[@Anne_Mahoney]

When Simon mentioned Georgia I assumed at once he was talking about the golf course at Augusta -- we know golf is his biggest passion, except *possibly* for sudoku, right?

[@longwaytotipperary]

@@Anne_Mahoney It is a gorgeous golf course - particularlly in April during the Masters when the azaleas are in bloom!

[@Cairful]

"I've got wallgreen" has to be one of my favorite deductions ever 😂

[@longwaytotipperary]

I immediately thought of the drug store/multipurpose store. Do they have Wallgreens stores in the UK?

[@shadowfox1221]

@@longwaytotipperary We don't, it's a US exclusive. Our equivalent is Boots. Interestingly, Boots and Walgreens are owned by the same corporation.

[@longwaytotipperary]

@@shadowfox1221 Ah... Thanks for the reply!

[@cameronhendricks5967]

I used to use this channel to fall asleep to, but haven't watched in a while since I fell out of Sudoku. But God your content and your disposition is so good please keep doing what you are doing!

[@gregs2284]

I love how at 53min in he's done all the Nurikabe and all the Killer logic and all he has left is plain old Sudoku -- and that's the point where Simon seems completely stumped, "I don't know... I don't know... Golly, ummm"

[@SSGranor]

In fairness to Simon, it's not a particularly simple bit of sudoku logic right at the end there.

[@markp7262]

50:41 finish. I couldn't see any other way to solve that end, although I took it the other way around (through row 6) and got dueling 8s in row 4. Another awesome puzzle!

[@PigInPJs]

I somehow read "even" instead of "odd" and managed to solve that version haha. Happy that there still was a solution for that mistake.

[@LazerWulf]

I mean, it makes sense, that square was probably to disambiguate that square from being a 6 or 7. If the version where it's a 6 wasn't a valid sudoku, then there would no need to disambiguate.

[@PigInPJs]

@@LazerWulf There could have been multiple viable versions with even numbers though. That would have made it impossible to solve.

[@LazerWulf]

@@PigInPJs Was there any point on the solve path where you had to bifurcate? (other than the even/odd square)

[@PigInPJs]

@@LazerWulf I'm not entirely sure where to draw the line between bifurcation and logical elimination, I don't write down numbers that I don't feel sure of (because I hate erasing haha) so I guess that makes it a no? But I tend to be able to follow quite many steps mentally, so I don't know if that helps to tell wether the odd version of the sudoku was better/easier/more elegant than the even version. My solve path was really very similar to Simon's as far as I can remember. I could place the 6 in the even/odd-square at the point where Simon could conclude that the 28-box in that corner had to contain 1,5,6,7 and 9 (at 25:55), where Simon still had all the options of 1, 7 and 9 for that square... but it didn't really result in much of a difference to be able to place that digit at that point, I still continued the solve very Similar to Simon even after that if I remember it correctly. I got the 5 in the 29-box out of it ofc, but then I went on with the 8, 5 and the 3 in the last column just as Simon did, and then the 10-box based on that 8.

[@LednacekZ]

my idea for the last pattern is this: No.1 It does not matter what is in r6c6, either way r5c6 is a 6. If you put in a 1, the solve bounces over in row 6 until it jumps into row 5 where r5c3 turns in a 9. No.2 r6c6 cant be a 9, if you put it in the solve bounces around in row 6 and in the puts two 6s in row 5.

[@terry9819]

For the end of the puzzle I noticed that if r5c6 is a 9 you get two 7s looking at the 78 pair in box 5. Alternatively if r6c6 is a 9 you get two 8s looking at the 78 pair. Took a while to spot so I'm not sure it was that much easier. Thanks for another enjoyable solve.

[@LittleBallOfPurr]

Nurikabe Sweeper is an awesome recent puzzle from KNT, Sea and Islands theme!

[@OlafDoschke]

59:52 - I can't. I got stuck at it, too. I've seen the pinned comment of SSG. Is there a name for that? It has to stretch 3 boxes. 1 box has an ab pair, and in the 2 rows (in this case) of that pair, the two other boxes pair that once with ac and once with bc. So in one of the two cases of filling in the ab pair the other boxes cells both become c (that's why they have to be in two separate boxes to allow that case) and the only thing preventing that is c not being able in the third row of the box with the ab pair. I guess there is a name for it, as anything in Sudoku has names. But I watch this channel for >2 years by now, I haven't seen it before. Bent triples, sky scrapers, all kind of fishes and Star Wars references, yes. But that? A Jar Jar Binks, is it?

[@jessochberg4034]

Simon, please commission a mug with your face and the word “Bobbins!” Printed on it! 😆

[@ianoz1]

I got to the home stretch & chose to "resolve" the 1-7 pair in grid 6... one way breaks, the other doesn't. Your way was more "logical".

[@OlafDoschke]

48:50 One question about that: When you see one triple of numbers (123) strinping (here in boxes 1-3) then the other triples of the boxes also stripe, isn't that a rule? Without knowing that you can still deduct the 8 in box 2 has to be in row 3, so r3c1 reduces from 789 to 79. And there has to be an eight inn row 1 of box 1 just like there has to be a six in row 2 of box 3.

[@chrisbattey]

The easier way to solve box 1 is to think about how to fill the region once you've assumed it has size 4 - we have to find homes for 1, 2, and 3 somewhere. Placing the 4 means r7c1 becomes a 3 with a 1/8 pair on top of it, which means, in combination with the 2 logic you'd just done, none of 1, 2, or 3 can be in c1 - which quickly forces you into the same contradiction you found with the downward L shape.

[@Coyotek4]

I had an absolute brain-fart on this one. I spent over 90 minutes on this, and stumbled across the solution by guessing. Not satisfied, I went back to where I guessed and spent more time trying to see what I missed. Eventually, I gave up and started watching the video ... ... and it was around halfway that I saw what I erred on: I somehow thought that 2 plus 8 could equal 6. [Specifically, I pencilmarked r1c5 as "14" instead of "18".] That error corrected, I did actually find my way through. But *yeesh* ... Total time spent on this: 1:51:03. Nice puzzle!

[@Harrery]

Is it possible for Sven to add the killer calculator to these online puzzles like the phone apps have? I use the calculator frequently and it would have made figuring out the 28 cage being 5 with 1679 much easier since you could visualize all of the possibilities and eliminate them one by one. I sometimes open the killer app while working on a puzzle like this for that reason

[@de8o]

Over 1 hour for the video. I know I’m not going to be able to solve this one.

[@EliChristman]

Me too. Cue the people who say they did it in a fraction the time that Simon did it. ;-)

[@brook316]

When it's over an hour, I know i'm gonna struggle to follow the bloody video... haha

[@SSGranor]

@@EliChristman Well, for what it's worth, I spent quite a few hours on it. 😉

[@mikedonnan6541]

Absolutely! Popcorn, beer, relax and watch Simon work his magic! 😃

[@MrTurner999]

I don't even attempt a puzzle if the video length is this long. I just enjoy Simon's solve while thinking, "I would have never spotted that"

[@jaelikesjackalopes]

You should start using undo to go back on conjecture to prevent lingering errant pencil marks.

[@piarittersporn]

This was a very exhausting but brilliant puzzle. It took me a long time and from time to time I didn't get any further or made mistakes, so that I had to steal a gray cell from Simon.

[@MonsoonMike]

As regards the game, what I spotted at the 59:47 mark is thus... If R6C6 is a 1, then R6C7 is a 7, R4C7 is a 1, and now the 7 in row 4 must be in R4C3, which makes R5C3 a 9, which means R5C6 cannot be 9. And of course if R6C6 is 9, R5C6 cannot be 9.

[@wariolandgoldpiramid]

49:07 I think there's Roping in Boxes 1-3 !

[@solfeinberg437]

58:00 was stumping me. I tuned in to see how Simon solved it. He seems to be down on himself. I'm waiting to learn something new. At that late point, it would be very easy to bifurcate. You wouldn't prove uniqueness if you solved it, but assuming uniqueness you'd have it. Or you'd run into a contradiction and eliminate your assumption. It's very short - so easy to do - but hard to see.

[@maljamin]

The simplest I could see the end: there are two spots for 8 in row 6, two spots for 7 in row 5, and two spots for 9 in row 4. But one choice for 8 would drive 9 into both spots in r4: one forced directly in box 6, the other via how 7's get displaced. Yeah, wish it could be simplified and named some kind of sea creature.

[@maljamin]

Here's another go: There's a 7/8 pair in box 5. But 7 and 8 are each in pairs with 9, in boxes 4 and 6 respectively. If you put the 7/8 pair in the wrong order, they force the outer 9's to be at the tops of the outer boxes. Ugh. I can feel the resemblance to other patterns but it's so hard to visualize and retain.

[@maljamin]

Take three: 9 is paired with 7s in the left box, and paired with 8s on the right. In the middle is a 7-8 pair that always forces the other pairs. In the right order, they relieve the pressure taking 7 and 8 from the outer pairs and stopping 9 from having to be at the top of both outer boxes.

[@_-_-Sipita-_-_]

1:01:45 for me. halfway through i was strongly forced to guess, and did it correctly!?! looking at the solve, at 38:17, i attempted to see what happened if R1C9 was 2, and instead of using the region i just put it as a 4 and kept sitting there.

[@ericpraline1302]

I like sudoku and I like nurikabe so was always going to be partial to this. At one or two points felt I was veering dangerously close to bifurcation - I probably missed some logic. No doubt Simon will elucidate.

[@G.Aaron.Fisher]

Brutal puzzle. Two hours for me.

[@kenross4453]

@32:00, remove the pencil marked 8's in C1 so it won't bite you later! Also, a few seconds later you put the 5 into R5C1 when it should have been R6C1...

[@geoff544]

39:24 - I seem to have an 8 in one of those cells - why is that? - oh yes, bifurcation! 🤣

[@RockyInSea74]

Best logic I found for the end was to look at R4C3. If it is 7, then R4C7 is a 1, which makes R6C6 = 1 through X-wing. If R4C3 is instead 9, then R4C8 is 8, which gives R6C8 as 9, and again makes R6C6 = 1. So R6C6 is always 1 no matter which value R4C3 has. Then it all chains out.

[@barneytrubble]

I found that putting either a 6 OR a 9 in R5C6 would end up forcing a 1 directly below it in R6C6, so I placed the 1 and was able to finish the puzzle.

[@Gonzalo_Garcia_]

40:53 for me. Nice puzzle!!

[@paulwright13]

Is the BUG (uniqueness constraint) a proven theorem? Ie if all cells have 2 choices except one having 3, does it mean that cell is the the one that repeats 3 times?

[@ca-ke9493]

33:04 theres a 5 in that row!!

[@fornife5004]

Did the grey circle in the bottom right cell matter? It only ruled out a 6.

[@SSGranor]

Yes. Without the circle r69c79 would be a deadly pattern on 67. I put the circle in because I couldn't find a straightforward way to change that without redoing massive amounts on the puzzle's logic.

[@matthewjohnson6360]

What do you mean when you say bobbin?

[@kyleborders420]

how do you even start this puzzle?

[@headoftss]

Was the circle in r9c9 actually used?

[@SSGranor]

Yes. If you don't use it, you end up with a four-cell deadly pattern in the end.

[@timotab]

Yes, it removed a 6

[@mister-8658]

Let's go

[@G1uckman]

I tried to solve it 7 times. Every time I went to similar mistake (in blocks 1 and 4). After watching solution I still can't understand how I made one mistake 7 times.

[@stephenmccarthy1795]

His solution is equivalent to there being an x-wing on the nines.

[@Playingwithproxies]

Are their ever any that don’t have normal sudoku rules apply?

[@wariolandgoldpiramid]

there have been some puzzles, yeah. And they can get really weird.

Isn't this a BUG pattern (Binary Universal Grave) at the end of the puzzle? Just remove 6 from r4c6 and it solves... Nice puzzle and solve as always. Edit: Sorry, this was already mentioned in earlier comments. I watch the videos mostly two weeks delayed... But i think this is not a kind of cheating or biforcation, because there are only 2 possibilities left for all cells with two pencil marks, one of the pencil marks must be correct and that is the way Simon solved the puzzle. Anyway interesting and entertaining stuff... Edit2: Uniqueness is of course a valid way to solve, especially in speed solving, and because Simon explains the logic every time it occurs. So why not use it?

[@Unchained_Alice]

He wants to not only solve but prove that it is unique. If you use uniqueness it assumes it is unique already. So if you go into it without that assumption you can't use it. It's fine to use for speed solving but I agree with Simon that it isn't good to use otherwise. It can make a harder puzzle too easy sometimes.

[@wariolandgoldpiramid]

Simon explained it in one of his recent videos - he wants to solve the puzzle as if he is the first person who is solving the puzzle. By using uniqueness, he is having an advantage that the puzzle testers didn't do, and he considers that unfair.

[@pokertroll320]

I don’t see where the ruleset specifies that clue cells cannot be shaded.

[@RichSmith77]

How about "the digit placed in the clue cell must equal the number of cells in the cage". That's going to be difficult if it's not in a cage.

[@Swynndla]

"Each unshaded region must contain exactly one clue cell."

[@ApesAmongUs]

So... I can write a 2 into the 5 cage and then state blankly for a while.

[@e7diablo]

Is nobody else going to question why South Park/Cartman is in the thumbnail??

[@megaminxpll]

The BUG+1 = bi-value universal grave technique solves this in the end. Ie r4c6 must be a 9.

[@SSGranor]

BUG's a uniqueness technique. It's only logically valid if the puzzle is otherwise verified to have a unique solution, which Simon and Mark generally try not to presume in their live solves.

[@molaeiali]

Link is getting 404?

[@daniellydford6142]

Seems to be working now.

[@LazerWulf]

Long ago on this channel, I remember you told us of a technique called the B.U.G. I don't remember what it stands for or how it works, but I think I remember that it applies if all the remaining clues are narrowed down to 2 choices, except for 1 square that has 3, so couldn't you have used that to solve the end?

[@murkbaccafett2187]

I used B.U.G. (Bi-value Universal Grave) here, also. You cannot allow the puzzle to have all remaining cells with just two candidates or it will not have a unique solution. Thus, for the cell with three candidates, removal of one of them (the 9) would lead to this pattern, so it has to be the correct digit.

[@abdoroma6928]

Memorable to mention That black dot at the bottom left was useless 🤣

[@RichSmith77]

You may have a mark on your screen? There's no black dot in the bottom left. 🙂 (There's a grey dot bottom right, which is very much needed to eliminate 6 from there.)

[@abdoroma6928]

@@RichSmith77 sorry i ment right He doesn't need to eliminate 6 He found the digits easily Watch that again

[@abdoroma6928]

After rethinking He used it but I think it wasn't necessary

[@RichSmith77]

@@abdoroma6928 The puzzle constructor has replied to a couple of other comments saying you end up with a deadly pattern without it.

[@daveturner5305]

BUG?

[@_LOGA_]

I'm sure you have no clue who this kid in your thumbnail is :D

[@adipy8912]

59:52 How can we that doesn't see the simple way tell you what it is?

[@abdoroma6928]

Gg