Another Birthday for the Kopps?

Here's where you can try 21 by James Kopp: sudokupad.app/5c6uuvchca
Normal sudoku rules apply. Adjacent digits along the green lines have a difference of at least five. The clues outside the grid show the sum of the first X digits from that direction, where X is the first of those digits.
(James promises us not to send another birthday puzzle for the next two years!)
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Hi! We're Simon Anthony and Mark Goodliffe, two of the UK's most enthusiastic puzzle solvers. We have both represented the UK at the World Sudoku Championships and the World Puzzle Championships. We're also "cryptic crossword" aficionados. Mark is the twelve-time winner of The Times crossword championship and twice Senior World Champion in Sudoku, and Simon is the former record holder for most consecutive correct solutions to The Listener crossword. We hope we can help your puzzle solving while also introducing you to some of the world's best puzzles.
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Simon and Mark
▶ Contents ◀
0:00 Theme Music & News around the channel
3:00 Rules of today’s puzzle
4:07 Start Of Solve - Let's Get Cracking!

[@angec9908]

Re recognizing the the Dutch whisper thing yesterday, we don’t criticize. We’re just amazed at the mental gymnastics that you can go through to reach the same conclusion as the missed easy digit. We love your videos and would never criticize.

[@raysouth1952]

Found that a bit hard, enjoyable, but hard, at least for me. I enjoyed Mark’s solve too. Plenty of opportunities to shout at the screen!

[@praematura]

Finished this in 27:24 (conflict checker off); I think I made an assumption based on a gut feeling in box 3 that just happened to work out, however, so not sure I deserve that time! I found it amusing that Mark kept ignoring the 21 X-sums on the left that would have led to a faster solve, but he did find his way through without hunches! 😅 Wonderful puzzle from James, many thanks to him!

[@soulus98]

Was the assumption the 6 in r1c7? I made the same assumption and was flying, but I realised it may have been faulty and unwound. Took way too long haha

[@praematura]

@@soulus98 I think it was, to be honest! It was definitely a 'gut feeling' that I couldn't explain at the time, but thankfully worked out in the end!

[@WayneRossi]

The x-sum in row 7 was sitting there for quite a while. After the 2 was placed I was surprised that you never came back and filled in that the other digits had to be 7 and 8, which would’ve disambiguated the high digits sooner. All round enjoyable though, a lot of great logic.

[@mscha]

And during the endgame, it was an obvious 8, which would have made things a lot easier.

[@frankjiang1857]

Finished in 46:14. Got stuck near the midpoint, but with going down some paths, was able to figure out what had to be high and what had to be low. Fun puzzle!

[@Briteboy678]

Its amazing how you guys solve these puzzles i cant wrap my head around kiler sudokus let alone puzzles like this

[@franzelmagetower]

Excellent puzzle. Love all these 21-themed german whispers puzzles. 16:28 for me.

[@mrrobotman5299]

After determining that R1C6 can't be a 6 there's only 2 positions available for 6 in row 1, C5 & C7. If R9C7 is a 6 then R7C5 is also and you can't put a 6 in row 1.

[@scbl46]

Why does R9C7 force R7C5? Couldn’t R7C6 be a 6 also?

[@RecreationalCynic]

71:41 for me. I got stuck for a while and needed Mark's help to figure out the 1 line.

[@chocolateboy300]

I finished in 77 minutes. This was a pretty cool coloring puzzle with some cool geometry. I think my favorite part was deciding between two places for 6 in box 3, which r2c8 breaks by forcing r1c7 to be a 4, giving r1c5 to be a 6. This points to r7c5, which I had already ruled down to a 3 or 6, making it a 3. Now my 3 and 4 are on different colors, breaking my grid. Great Puzzle!

[@Kirbyfan87827]

Finished in 00:31:42 with help from the video.

[@MattYDdraig]

26:23 Lovely puzzle and some very neat stuff (technical term) between the X-Sums and whispers.

[@emilywilliams3237]

When I first saw the puzzle I thought I would try to solve it before watching. But I was short on time for watching yesterday, and when I discovered the puzzle was by James Kopp I figured I would watch first and solve later. It turned out I had to finish watching this afternoon and can report with great pleasure that you did marvelously, Mark, and I will put it on the 'maybe someday' list for my own potential solving. A beautiful puzzle, I loved how it all came together. And congratulations to England on getting through the quarterfinal against Switzerland and you will indeed face Netherlands in the next round! Maybe I'll watch! Edited to add: in reference to things you missed in prior puzzles or whenever at all - I would MUCH rather see you solve live, cold, having never seen the puzzle before, than see a walkthrough of a best pathway through a puzzle. It is a lot like sports, actually: we know the outcome of these videos, but it is still exciting to see the game actually played. Watching you (and Simon) solve, bringing your expertise and experience to it, but not any particular foreknowledge of the actual puzzle at hand, is fascinating to me. Thanks for making this channel about that.

[@tbi1161]

Nice puzzle, thank you for posting!

[@LednacekZ]

35:30 for me. i was quite slow. especially at the end.

[@grimsqueaker5333]

Thanks for the solve, Mark. ❤

[@tomgalli1188]

Ugh. Got started easily enough, placed a lot of 5s, worked the polarity of a few of the lines, even placed a few digits. I needed Mark's help to get past that initial success, though! I let him give me a couple of hints, and took advantage of his overlooking a couple of things, and came through in the end. I'll accept 80% success!

[@angec9908]

I ended up with a deadly pattern with 8 cells and no more clues! What did I do wrong? Oh that 21 clue never got done. Whew!

[@snjyjn]

I had a similar path to Mark's and got stuck at a point. I watched Mark till he got there, and around the 25:50 point, he deduced that the 3 cells in column 7 were low. Fantastic logic, but I found that the same logic results in R7C8 being a 6, which simplifies the solve from there very rapidly. The logic goes something like this: In R1, a 6 can only be present in Cols 5, and 7. In R7, a 6 can only be in Cols 5 and 8. In box 9, a 6 can only be in R7C8, or R9C7. So, if R1C7 is a 6, R9C7 cannot be a 6, and by box 9 logic, R7C8 must be a 6. If R1C7 is not a 6, then R1C5 is a 6, and R7C5 is not a 6. By row 7 logic, R7C8 is a 6! That leads to the 1 in R7C7, ...

[@darreljones8645]

I love the illustration on the thumbnail! Was that inspired by the Keystone Kops?

[@piarittersporn]

Brilliant puzzle.

[@psiphiorg]

Very enjoyable puzzle! My time today was 20:20, solver number 4115.

[@Gonzalo_Garcia_]

11:43 for me. Very nice puzzle!!

[@srwapo]

36:14, got really stuck on figuring out which way the highs and lows went on the green 1, feel like I did bifurcation to figure it out.

[@bait6652]

Nice to see mark deploy 2 coloursystem schemes

[@theredstoneengineer6934]

24:44 for me

[@reissjones4043]

Got 86.14 which is a long time but I'm just happy to have solved a CTC with no help from the video 😅

[@dahmann7588]

Is anyone else getting problems with sven’s software on ipad? Numbers keep disappearing.

[@wardtielens3677]

Yes, have the same problem the last couple of days

[@mikecurnock9483]

@@wardtielens3677yes. Having to use safari

[@derekswager]

there was a ~8 min of having 3/4 of the digits on the left x-sum lol, still an impressive solve as always

[@siorge]

My comment will probably go unread, but the app is constantly bugging on mobile. Clues and candidate numbers keep on disappearing.

[@rollinginthesnow]

Same for me

[@EkuuleusNorth]

hard for me but eventually got there.

[@donkeykong6805]

What are x sigita

[@bait6652]

Thats disappointing, was hoping the D5lines would force some more lettering/coloring and cages but midway u do need to deploy the cages. Whats interesting is that the D5 2&1 shapes...forces 4 H/L in specific row...and quick work eliminates all but one. But going from the D5-2&1 to the corner D5s is hard. In the end ur left w B258 being rather sparse and the cages go to work.

[@inspiringsand123]

Rules: 03:05 Let's Get Cracking: 04:05 Mark's time: 35m57s Puzzle Solved: 40:02 What about this video's Top Tier Simarkisms?! Three In the Corner: 2x (28:03) Knowledge Bomb: 1x (02:42) Numpty: 1x (35:55) And how about this video's Simarkisms?! Sorry: 7x (01:12, 06:22, 17:39, 18:32, 21:34, 33:36, 35:12) By Sudoku: 7x (05:32, 32:06, 32:12, 38:51, 39:00, 39:06) First Digit: 4x (03:47, 03:52, 06:34) In Fact: 4x (07:09, 14:00, 35:04, 36:35) Hang On: 3x (16:32, 24:28, 25:39) Obviously: 3x (01:20, 08:10, 10:35) Ah: 3x (16:32, 18:15, 31:53) Goodness: 2x (27:50, 30:44) Brilliant: 2x (01:35, 40:02) Missing Something: 1x (17:39) Stuck: 1x (11:10) Beautiful: 1x (19:19) Fascinating: 1x (04:03) Deadly Pattern: 1x (39:34) Wake Up: 1x (27:18) What Does This Mean?: 1x (22:55) Pencil Mark/mark: 1x (09:02) Most popular number(>9), digit and colour this video: Twenty One (17 mentions) One (96 mentions) Orange (16 mentions) Antithesis Battles: Low (48) - High (40) Even (2) - Odd (0) Column (19) - Row (18) 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!

[@werefrogofassyria6609]

all that talk of using the 21 sums, but you ignored the 21 sum that just needed one more digit put in.

[@tBagley43]

really not a fan of the constant mark-bashing that goes on here. for each of his solves it feels like everyone immediately races to the comments to point out some tiny thing he missed that could've saved a couple of seconds. in my estimation he and simon make mistakes at about the same frequency, yet simon doesn't seem to receive anywhere near the same level of scrutiny. anyway, 1:54:15 for the puzzle, probably bifurcated a bit too far at some steps but definitely wouldn't have solved it otherwise

[@joekerr3638]

July 8 2024 on the x sum clues?

[@user-se8fo8vg7j]

You completely forgot the third X sum in row 7. The time taken to solve could have been shortened by a few minutes only if you remembered the third X sum clue.

[@ericveneto1593]

Mark, just as an aesthetic thing, I prefer you use the Wimbledon colors *green/purple) when you haven’t determined high/low.

[@ericveneto1593]

I obviously meant green/pink

[@zobososhizion6478]

01:44:53 and I'm pretty sure checking your video is cheating.

[@joeshonk9715]

Deja vu