Our Hardest Sudoku And How To Solve It (Slowly!)
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- čas přidán 14. 01. 2019
- One of our "kind" viewers suggested we give this incredibly difficult Sudoku a try. Apologies for the length of the video but Simon's brain couldn't go any faster! Lots of advanced techniques required here including our old friend, the Swordfish.
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Amazing how you spotted the Swordfish and Empty Rectangle with only a few candidates written down!
Also your ability to find chains is incredible.
Around 29 minutes I thought you were spending a looooong time thinking.
Then I realised I'd clicked away from a scan popup and had paused the video for a couple of minutes! :D
lmao
hahahahhahaha
empty rectangle, swordfish, finned X wing, Y wing, and lots of chains? please don't apologize for such an amazing, well informative video
I didn't know that some hard sudokus required the solver to look so far along the chain of consequences. I've resorted to starting a chain to see if it breaks but always with the feeling that I was missing something that indicated the next logical step. Anyway, after watching you breeze though some very tricky crosswords, it's nice to see that you're human.
Really enjoying your videos.
Don't take this the wrong way but I use your videos to fall asleep!
he does have a nice monotonic voice that doesn't fluctuate too much (which, thinking about it, might be one of the reasons why I like watching him solve puzzles)
me too!
🤣🤣🤣
me too - it overloads my brain and I shut down, just like a computer
Me too
Please don't apologize for delays from momentarily blanking out during "live solves" - by verbalizing your thought progress as you step back to re-assess the solve, you provide a valuable lesson when hitting a brick wall : have I missed something obvious? are their any potentially useful distribution patterns to be spotted? etc. Very useful indeed! Thanks for a great video - learned more than few lessons from this one.
Thanks for the amazing sudoku. Took me 06:46, that's in hours haha... Did learn 3 new rules because of this!
What rules
This was very enjoyable! I especially liked the on-screen editing!
Fantastic. These brutal Sudoku's help a lot because you are forced out of all the standard stuff you do and watching how you seek and find the 'get out of jail card' really helps me to tackle and solve those puzzles that in the past I may have given up on.
Learned a lot from this. I like that you do your standard notations where blocks are limited to 2 numbers, you do not charge ahead and fill in the rest if the numbers. You use logic all the way through. I do all the initial notations as well, but tend to fill in all the numbers afterwards, making my puzzle cluttered, blinding me to X-wings and fishes. I appreciate your channel.
I enjoy your videos, and it's nice to see that the techniques I have discovered are sufficient to solve very hard puzzles. I try to avoid "pencil marks" on my paper puzzles, but sometimes they become essential. Thanks for doing these; they are very entertainig.
You, sir, are a Sudoku wizard! Those chains that you did was superb logic and i have no idea how you were able to spot that
Amazing solve! Thank you for sharing it
Thank you for showing us. This is incredible and I've learn new techniques.
Fantastic! I learnt quite a lot from this puzzle!
2019 Simon: "I'm already a half an hour in", apologizes for the 40 minute video.
2022 Simon: "Oh, you sweet summer child!"
I saw the 1-6 pair at R6 C6 earlier but didn't know enough about chaining to use it but you presented it clearly. Thanks as always Simon :)
I ran this through the Andrew Stuart solver starting at the point where you invoked chaining. That solver was forced to use multiple increasingly esoteric steps so I think your approach is well justified. Thanks for this, I’m now realizing that your approach to cracking this one can be a legitimate resort.
Thank you for the 40min sudoku!
Learnt so many techniques thankyou so very much for explaining so well will henceforth make sudokus much easier to solve
It is very valuable to see the overall process, particularly which part of the puzzle to move to when progress is not being made. This vid is also a good example of use of pencil marks and how it can be both useful and can easily get out of control. Don't worry about the length of the vid, some things take time.
Yes hardest
Thank you for solving slowly with logical tricks
Amazing puzzle. I solved it without any pencil marking in 40:37, the exact length of your video ! I spent eons working the potential variations in the lower chute based on the fact the 6 in box 7 was either in the southwest or notheast corner. All permutations always ended up with either a 36 or a 26 pair, establishing the 9 was in r9c2. Also, the 4 always ended up in r8c2. The impact of the 27 in the middle column of box 4 does marvels to separate the right and left sides of box 7 and clear the middle column. There was still quite a bit of work to do, but nothing so complicated. So no swordfish or empty rectangles or other beautiful things for me, but a solution in reasonable time for this difficult puzzle.
40 minutes long?
This is gonna be a fun one.
Learned a hell of a lot there - excellent
Wow a beast....I need to watch you think it through..thanks
Wow good brain training this one. I tried to use couple ALS instead forcing contradiction but it was even more bizarre, and i still had to force some chain in the end. How you're so fast that's amazing
I struggled quite a bit with this one as well but I didn't have to go through that large of a chain to get it solved. Took me about half an hour. One big change is that I had top left and bottom right solved a lot sooner which made bottom right easier as well.
Wow! I learned some things about how to follow chains from this one.
I am curious, compared to something like "easter monster" grid. how hard would you say this one is?
"Simon's brain couldn't go any faster!" - gave me a right giggle over there. Say, I've been wondering what that software is that you're using to digitalize the sudoku. Or is it just a website i'm missing?
Glad I didn't meet this puzzle in a dark alley or in a puzzle book - I am getting quite handy with 'hard' puzzles but I hit a wall with the notations and spotting required for 'expert' level etc.
I finally gave up after 4 attempts and just watched in awe
It can be solved without the techniques, if you pencil mark carefully & note the pairs/triples as soon as you find them.
That was a brain bender. I'm still having issues understanding triples and pairs (to an extent). And some of the exclusions you can make because of them. Once again, I followed along, paused quite a few times to see if I could figure out anything, then checked to see if I was correct. The experience you have is what I'm lacking, especially when looking at exclusions. Thanks again for the information you provided as you solved the puzzle and the thought process on the majority of your choices during this solve!
In the same boat, bro/sis. Watching him get frustrated made me to be less hard on myself.
nicely done!
Very good all your vídeos... Clear and full of knowlege... Tks a lot...
Is it possible to send a puzzle that I'm stucked for 5 days, to have a hint from you? If so, how?
Thanks for taking us on the complete journey. I've wondered, notation for chaining...is it true that if a chain returns to the original cell correctly, all the choices along the chain can be assumed correct. Have you ever seen a situation where you had to chain within a chain...,
Thanks very much...I'm really starting to enjoy this now. Where can I find android software that will allow me to choose difficulty level...?
Not slow enough, my head hurts, I’ll continue trying to understand this later
You can always slow the video in the parameter
I did slow it down and I still couldnt understand the way he explained it. At 8min 50 he said cif this square can "see" this square and this square! then it cannot contain a 7"WTF . What the hell did he mean by if this Square can "see" this square and This square? As Far as I know, the squares can't see anything . Does he mean if they are adjacent to each other they are on the same column or row what the hell does he mean by if it can see this Square in the Square. Clearly some terminology that I just don't understand. Although I'm sure it makes perfect sense can you actually explain the technique you are using as opposed to use the technique and put the answer in without explaining how you got there. Explaining where you got the can't see it technique in some of the video would be helpful for referring to another video would be helpful.
@@leeslater8891 Two squares can see each other if they are the same row, column or 3x3 square, in other words, if they can't both have the same number. At 8:50, he concluded either R1C7 or R3C3 contained a 7; in either of those cases, R3C8 can't contain a 7 (since that would conflict with either R1C7 or R3C3).
It can be solved without any of that stuff. More pencil marks, more consistently... logic you can hold in your head. I used no chains, just pairs & triples, etc.
@@leeslater8891 they intersect, share a column or row or block.
Fantastic well done
This puzzle was so so difficult - you are so good to solve it. I tried to do it but got stuck. Maybe Ariadnes thread would have helped me? Thank you
Noooooo.....you went for the chain check. I IMMENSELY appreciated your love of logic and and trying to crack all those triple options....nit to mention your hybrid pencil marks which I hate, too. Cheers anyway, mate!
Sorry not a sudoku person, why is the chain check seen as just 'good enough'? Is it sort of like a cop out tactic? I found it pretty impressive
@@joaquinsoliven7254 I find it more rewarding to logically place/remove candidates than to "guess" in a candidate option then running the chain. Anyone can plug in and go; it takes talent to figure it out.
Please correct me if I am wrong but at 27:00 you said a chain starting with the 1,6 pair in row six, column six would establish whether either that cell was a six or the cell in row five, column one was a six. Having established that the starting cell of the chain was indeed a six was it not then logical to resolve all the other 1,6 pairs immediately from that point. You said "please let that be useful" and indeed it would have been if you pursued the other 1,6 pairs. Then the puzzle begins to unwind more rapidly from that point.
I've seen a few of your videos in the past few days. I followed everything you were doing. Not this one. Some of it certainly, but there was a lot of how did you arrive at that conclusion. lol The part where you highlighted half the board I did follow, but only because you highlighted half the board. lol
You don't need to look for swordfish at 24:14, simple skyscraper from rows 5 and 9 eliminate the 6 from R6C9 as well.
You guys are eons past me when you can say "simple skyscraper"
There was another way to get the 2 in the bottom row: it was part of a rectangle with the other 3 corners being 1/6 pairs. So, it could not be a 1 by uniqueness. Even, not fully relying on uniqueness: because the 6 was ruled out earlier, it could not be a 1 either - if it were, in any solution all four corners of the rectangle could also be switched, giving 6 in that square which Simon ruled out from being a 6.
I really liked it. Although it is hard, do hard ones from time to time
Little numbers r not visible. Pl make it visible. However I improved in solving sudoku by regularly watching your videos. Your explanation is very clear n understandable. Thanks
At 34:10 you could’ve used the 1-6 pairs to come to the same conclusion much easier
That's exactly what I thought too. Just pick one and follow the chain because only one option will work fully through, so find out which one that is.
Can you explain how?
I too got the 1/6 or 6/1 in column 1 - and did actually pick the correct order 1 in the middle - and 6 at the bottom - but then made a mistake - and reversed the 1/6 - and again got wrong - went back to the original 1/6 and did eventually finish after quite a few attempts - need to review the swordfish, finned X wing, Y wing whatever they are.
@@bill7192 the puzzle can be solved without any special techniques... maybe used one x-wing. 13:51
Only tip I have is to complete all pencil marks, including any pairs or triples you find from the beginning. All the "tricks" become obvious logic problems that are easily solved. But that's just my method... I do not mark all possibles, however. That becomes mind-numbing.
Dig! This one would've taken me forty days & forty nights ...
That was a great chain of logic
shucks, I was doing long chains to solve this one also so then watched you thinking you had some fancy move(s) I did not see...turned out you didn't. Beast of a puzzle. those chains are pretty much impossible to see without filling in all candidates. I wonder how Tan Tan would do on a puzzle like this one. :P
You don't need a long chain.
Once you find r9c4 being a 38, it's easy to spot as to why it can never be 3. 3 affects the neighbouring box 7 the way you get a 1-3 arrangement in the c2 which ultimately affects r4c3 being 8 which, in its order, makes r4c4 a 3 (which is impossible since you have already put 3 in r9c4).
I love this video, man :D
Me too!
I always enjoy watching you solve. It helps me learn techniques and find some as well. Something I found (and not sure if it'll work past this) but around 15:20 and up to 16:30 when you were noting the bottom left square, you had placed the 128 in that area. You had created a 12 pair, as well as a 18 pair within the 3 squares. You could, by that logic, remove the 8 from the 12 pairing and place the 8 in the remaining square, but then do the exact same by removing the 2 from the pair that you had in the 18 pair and place it in the square it's left in, thereby placing the 1 and unraveling the puzzle a bit quicker from that point.
I'm posting this comment after solving the thing, but before watching the video.
Got to fifty cells filled, fairly quickly by my standards, thanks partly to my first successful attempt at identifying and using an empty rectangle (giving me the 4 in R8C2 - or B2 as I prefer to call it). And there I stuck. Not enough advanced techniques in my armoury as yet.
Once I gave up on finding a fully logical solution and opted for good old T & E, I needed less than ten minutes more. Strikes me that if you get to that sort of point in the solution, it can take just as much time finding a logical approach that works, as it can using cruder methods. And if time is of the essence - which I imagine to be the case in championship events - then either way is equally valid. (My attitude to competitive chess was similar - it's the result that counts, not the beauty of the game.)
Esoteric is definitely the word!
Great work for forcing chains.
Not watched the vid yet... I just solved this puzzle but I think it was a fluke... I found this weird chain of things which seemed to eliminate a 2 somewhere and solved a number, and then I saw a pattern in the bottom left which I looked at and said "if I put a 1 in here, I don't think it works, so let's put in a 7 and hope for the best..." and it worked. But I'm pretty sure it was just luck coz when I went back to that point, I couldn't find the 'logic' I used to come to that conclusion in the first place...
Oh well. Got there, kinda. I'll watch the vid and see how I could have done it properly.
I'm getting a little addicted to your channel btw Simon. Thanks for doing it.
OK, having watched your solve, I feel a little better now =0P
More accurate and pertinent use of logic than my 'solve', but still a bit of 'plug-and-see' work, heh.
Needs do, I suppose.... Well done.
At 27:50 i think you can resolve a 2 in R9C7 since from the chain described earlier R9C1 needs to be a 1 OR R5C7 needs to be a 1, therefore R9C7 can only be a 2.
Please correct me if im wrong
No, you are totally correct.
Instead why not use a proper chain and arrive at the same conclusion? If we assume r9c7 to be a 1and follow the chain 81-86-76-61-61-31-31-41-42, we get the same result, ie r9c7 can only be a 2. I thought this would be more convincing.
Amazing
Could you please add the link to this puzzle so we can try to solve it? Thanks!
instead of dodging about all over, I would suggest reviewing the whole domain using 1 thru 9 in each direction. It is much better to be organized.
Or some explanation of priorities, like starting with areas with the most numbers or with a number that is repeated more than others in the given.
I am systematic, too, but I find I miss things if I pencil mark in numerical order all the time. And I prefer to solve all obvious cells first before marking.
I do not limit myself to only 2 per cell, if the number can be placed in 3-in-a-row in a block because it makes clearer which cells are blocked out in adjoining blocks. That's too much to keep in my head.
I also pencil mark all discovered pairs from the beginning... makes finding double pairs, x-wings or y-wings easier for me.
I pencil mark the entire puzzle before I watch Simon. And sometimes I solve all or as much as I can, then turn the video back on.
It is a problem when Simon is incomplete in marking or makes a stray error... like this video twice. I would think some ppl don't realize he's made a mistake & doubt their own eyes! 😳😄
I need to get in touch with you to understand few things regarding sudoku... Please help me
Can somebody suggest what app he is using?...or some good apps to solve costomize sudokus
The app used in this video is Duncan's SuDoku Solver
18:10 at this point you could've used uniqueness on the three 1-6 pairs to figure out the 1 is impossible on R9C7, which reveals a 1-8 pair in that box, removing the 1 from R8C2 and revealing a 4 that leads to a bunch of other numbers.
edit: 34:17 well you said it yourself! hahaha
Can you explain more how the three 1-6 pairs lead to elimination of 1 from R9C7?
what program do you use for this?
I have the same question! I wanna try this sudoku as well where you can add pencil marks
@@ariffumbreon5946 Duncan sudoku solver
Pardon my noobness, but at the 28:30 mark, he has a 178 pair in column 6 row 4 and also column 6 row 9. Should that not mean that the 78 that is repeating in column 6 row 5 should be removed....leaving a 4? At the end, it's clear the answer is no, but why not?
I didn't understand why there couldn't be a 6 in row 9, column 7. I must have missed, or misunderstood your reasoning at some point, even though you eliminated that possibility quite early (before you discovered the swordfish that eliminated the 6 in row 6, column 9). I'd be grateful if you, or someone else, could explain it to me.
because there is a 6-7 pair in the same 3x3
We could have found the 2 in r9c7 with uniqueness on the square r9c1 to r5c7 ( 1/6 s) and eliminated the 1 from r9c7.
@@CrackingTheCryptic hi here a not unique rectangle on the cells R5C1, R5C7, R9C1 and R9C7 because for 4 blocks the technique works only on 2 blocks only look a the video a 6 minutes 52 sec czcams.com/video/m634uHyIlis/video.html
Moncouer111 - sorry I’ve just reread your comment properly and it is very erudite. I will probably do a follow up video myself discussing this in more detail.
Yes good spot. I was clearly tired as I didn’t even discuss this in the video. I’m relieved I didn’t use it as the follow-up comment from moncouer111 below is quite right. Ie because the three instances of the pairs 1/6 are in three DIFFERENT 3x3 blocks, uniqueness can’t apply (because in any one of those 3x3 blocks one of the other 8 numbers could impose a relevant restriction on the 1/6 square).
would love to know the sudoku application used.
Duncan's SuDoku
The 7 dude!!!
That flailing cursor is going to cause a seizure. You've improved since this video was published.
6:30 how do you get to the 1 and 7 pair in r3c8?
c8 needed 1,6,7,9 and that square couldn't have a 6 or 9 making it either a 1 or a 7.
@@ShadowMark474 oh yeah, thanks. I completely missed that for some reason
a 1 8 pair setup at 17 minutes is noticable in the bottom row.. 2 has to go in one of the two slots in row 9 making the 1 2 8 a 1 8.
It also had a 12 pair in column 7 in addition to the 18 pair in row 8. meaning the 2 is placed in r9c7, the 8 in r8c9 and the 1 in r8c7
Could you guys please elaborate? I don't see how this triple eliminates anything.
Woah
At minute 18:15 when determined that R5C7 was a 1/6 and asked if that cracked it, it seems it might have since both R5C1 and R9C1 are also 1/6. Therefore, R1C7 cannot contain a 1 or a 6 (for uniqueness), so it must be a 2 which you didn’t place until minute 34.
JohnTLittle hi John, I’m actually going to do a separate video on this very point. Some very good solvers have made the same point you’ve spotted but we need to be extremely careful with uniqueness. Here because the 1/6 pairs would ALL be in separate 3x3 boxes we cannot use uniqueness for reasons I’ll explain.
I solved it in almost 30.minutes without pencils marks. Really proud. Thanks for editing brain torture like this
You gave up on the 3s too early had 2 places solved and was screaming at the phone for ages lol
Yup... or not marking 4s in block 7 early on... he just gave up on that block & row 2 too soon.
Wow! That was a hard one. (twss)
"Chaining" always struck me as just a fancy term for "guessing". You guess an answer and see if it breaks everything. Not saying I could do better, just the it feels unsatisfying.
Paxtez it’s more along the lines of “conditional logic”. You’re not guessing, rather, trying to see if anything is true regardless of which condition is picked. You’re not always looking for a contradiction.
@@jkid1134 I get what you're saying, and I would agree for things like x-wings or swordfishes. In the video, he literally guesses for the answer for it, and follows the path for the now forced answers, sees that it creates a contradiction, and realizes that it must be the other way. You could do that 'logic' for any time it is 50/50.
To me, this is different than other methods like x-wing where either state of the schrodinger's answer leads to the same end result. X-wing says 3 must be in this row, so we can exclude it from other cells in this row, that is a good logical inference. To borrow from physics, to me as soon as the answer is measured and and the quantum state collapses it is no longer "logic" but rather guessing.
I don't know if this would be solvable without guessing/chaining, I didn't try it. Also I am not saying it is wrong to do, just that it never felt good to solve one with that method.
Paxtez I’m not sure about this but I think there is logic that can be used in every situation but some logic is so complicated and situation that it isn’t worth it to remember it and look for where it can be use. A good example would be the computer solvers that tell you each step, it’s possible to be done purely through logic but at the end of the day (especially for humans) it is faster and less of a hassle to just guess when the logic required is overly complicated
When it comes to sudoku...."logic" is just a fancy term for "guessing"
Rules like "X-wing" are just common patterns where the guessing and contradiction-finding has been done ahead of time and packaged into an easy-to-apply form.
The problem is with the word "guess" itself. When you say, "It can't be a one because there's a one in the same row, and it can't be a two because ... " you're "guessing" that it's one or two and eliminating the guesses by checking. The so-called rules of Sudoku say you can't use trial and error, but you can't use anything else! I guess the only thing that's really forbidden is guessing without a plan, so that you have to solve the whole puzzle before you see your guess was wrong. The little numbers a solver writes in the boxes are all guesses, every last one of them.
The computer solver shows that there exists more than one solution.
I have watched over and over, and I still cannot see how you prooved the R3C8 could not be a 7 at around 9:00.
Start at 8:34
either R3C3 or R1C7 must be a 7
I'm a novice, so it took me a few times watching it as well. The "Y-wing" looks more like a triangle to me, with the 3 points having the following configuration: X,Y...X,Z...Y,Z. The first point (X,Y) must be able to "see" both other points, such that no matter what number is correct with the first point (X or Y), one or the other 2 points will have to be Z. Therefore, any other cell that can "see" both of the other 2 points (X,Z and Y,Z) cannot contain a Z. It's quite clever. The tricky part to me is spotting such a pattern. Practice I guess. Definitely trickier to spot than an X-wing (which I also just learned).
Well, not slow enough for me already at 9:11. Can't understand how you eliminated the 7.
He explains at at 8:35
Hi, Do we paid by playing sudoku?
yea.. no
yes.
Wow. Forty minutes long and he even paused the recording at least once at 21:22 mark 😄
Edit:
Spotted another cut at 30:17 mark 😂
38:40 I think you may have got lucky here. Cause I think that C6R9 was a 1 or 7 or 8 instead of 1 or 8…
If you watch the video again carefully, you will see how he logically eliminates the possibility of 7 being in that cell.
Why did he come to the conclusion with 1 and 7 at 06:33?
Column 8 needs: 1,6,7 & 9.
Upper right hand square already has a 9
Row 3 has a 6
6:33 square can only be a 1or 7
In row 3 col 6 is 9 and have been for quite some time as the video count goes on……
This is a nice and quite hard one but nowhere near what hardest would look like (actual difficulty around 8.6).
If you really want to see something beyond typical diabolical and insane ones (actual difficulty beyond 10) here is an example:
0,0,1,7,0,0,0,8,0
0,9,0,0,0,0,3,0,0
8,0,0,0,0,6,0,0,1
0,0,2,0,0,3,4,0,0
0,1,0,0,5,0,0,2,0
7,0,0,9,0,0,0,0,0
1,0,0,0,3,0,6,0,0
0,0,9,0,0,0,0,4,0
0,5,0,0,0,4,0,0,8
Try this one: ....48..5..31..69.........7.96..31..8.......3..16..45.6.........27..65..1..82....
@@keniangervo8417 10.3, nice
29:45 you said we have 147 triple, but actually we don't, 147 can only go into 2 squares, no?
That was hard
you say slowly, where exact is the slow part
C1R3 was a 2 at 4:30
Could also be c3r3
Thanks for your comment, first I thought you were right and I'd made a mistake, but no it could not be C3R3 and here is why: If you look at the grid carefully at 4:30, you will see that after C1R1 was revealed as 3 , there were four numbers left to be placed in C1 which were 1,2,5 and 6. Well, 1, 5 and 6 could not go into C1R3, because they were already inside the 3x3 box, therefore 2 was the only option for C1R3
@@nihatbekiroglu8004 yep youre right
The 1,6 pair in row 5 removes the 6 in row 4, column 8. You missed it very early in the game. That would resolve the 1,6 pair and continue down to row 9 for the 1,6 pair, making it a 6. But I certainly could not do the puzzle as well as you've done it. I still spend hours filling in all the squares possibilities, but am trying to utilize the Snyder method of finding squares with pairs.
Sorry. I don't get it. Could you be so kind to explain it to me? Why 1,6 pair in row 5 removes 6 in row 4 column 8? I used to solve medium/advance sudokus without any knowledge of these advance techniques. Now that I learn some of these, I get so excited but my brain can't get much of this stuff. I used to utilize the Snyder method for my own, because I realize myself that having to much numbers on one square it's a lot of work and make everything so crowded!
Its so easy
Ya idk what took him soo long. I could do this in 5min easy.
How did I do this in just over 13 minutes when the video is over 40 minutes? I'm not good at recalling all the moves after a puzzle is solved, but I know I used nothing beyond basics.
You blundered somewhere, like missed a possible digit, and your blunder turned out to be correct. In other words you bifurcated without knowing it.
Here is a puzzle that claims to be an 11 level of difficulty (on a scale of 5). The solution is provided on a link within the article apparently. I am by no means a master and have not tried it myself.
I was going to send this in via e-mail but could not figure out how to do it.
www.telegraph.co.uk/news/science/science-news/9359579/Worlds-hardest-sudoku-can-you-crack-it.html
Yeah that one is 11.6 because it has one Dynamic Forcing Chain and one Dynamic Unit Nested Forcing Chain. Without the later it would have been only 9.1 and without both it would have been only 7.2 so lower scale diabolical difficulty.
It is arguably possible to create harder ludicrous difficulty. One "only" needs to construct Advanced Dynamic Unit Nested Forcing Chain which basically means one need to go through multiple Dynamic Forcing Chain that are nested to eliminate at least 2 candidates in a unit (cell, row, column or box). Ofc in reality that is incredibly difficult. ;)
Imagine making a mistake along the way and only finding out at the end😬
If you make a mistake at the end you can follow the logic backwards to fix it. :)
REMINDER to fellow-viewers: if we can't help with $, we can at least remember to LIKE.
I am enjoying following your logic, but run it at half the normal speed of video because my brain is not as quick as yours. Your pointer, however, moves over the grid too fast even at half speed