Tangled in a Sudoku Web

Normal sudoku rules apply. Cages show their sums. Digits cannot repeat along marked (purple) diagonals. The blue line must have equal sums for each box the line passes through. This total may be different for different lines.

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▶Credits◀
Music: Tim McCaskey (Guitar) or Lucy Audrin (Piano) or Riffclown plays Mozart's Sonata no 16 ("Sonata Facile")
SOFTWARE: Thanks to Sam Cappleman-Lynes and Sven Neumann for their work.
Logo: Melvyn Mainini

Opening Credits: Joel Blundell

▶ABOUT US◀
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 championship 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.

Thank you for watching!
Simon and Mark

[SweDennis]

I can't really put my finger on it, but this was an absolute favourite solve from CTC. Something with Marks explanation, how the logic evolved with a very elegant setting and solution. Great one, Mark!

[emilywilliams]

This puzzle shows that a beautiful and elegant puzzle does not need to be very long or even all that complicated. Yes, it was tricky, I felt, and not simple, but it was quite easy to understand the logic as Mark explained it. Thank you, Yarr, for this puzzle! And Mark, I had to laugh at "the dichotomy of ways this trichotomy works ..." and then you said that you did not know what you were saying - but it was very clear to me! A fun and fascinating video. Thank you.

[rontyson]

These puzzles have me staring at them for 2 or 3 hours at a time. Sometimes I give up. Sometimes the puzzles does. But these guys Mark and Simon always defeat the puzzle in no time. Brilliant minds. :)

[jamilhaidarahmad]

"if I was a lunatic person called pencil Mark" made me laugh out loud

[doug]

Nothing give me more satisfaction than seeing Mark pencil in the same stuff that I did.

[ypkoval]

Mark, thank you for featuring my puzzle on the channel. I liked your solve as much as I liked to create it. Few things to mention: the "dichotomy" logic placing 5 in R5C3 is unavoidable and exactly as intended. The break in was supposed to be SET based. The sum of 12 cells you highlight on 25:35 equals exactly the sum of all the killer cages i.e. 40. Which means all they are all 1, 2, 3 or 4. This is proven by 2 extended Ph.-rings

[Ardalambdion]

I love puzzles that tell a deeper story than just maths and logic like this one.

[wossaaaat]

Top form on this one Mark. Ploughed your way through some tricky and very pretty logic at an impressive pace.

[Gliperal]

Wanted to point out a different way of looking at the break-in Mark found: The line total + R3C456 = 38 by box 2. And 2 times the line total + R3C456 <= 17 + 35 by rows 2 and 3. Subtract the two equations and you get that the line total is maxed at 14, which simultaneously forces the 89 pair in row 2 and the 56789 quint in row 3.

[keyaanmatin]

I somehow managed to use versions of the expanded phistomofel ring to place 1234s in boxes 1, 3, 7, 9. Coupled with Mark's logic with the box sum line at the beginning led to a nice smooth solve. What a lovely puzzle, I must say.

[danielcamp]

What an aptly named puzzle. I found myself getting stuck in seeming dead-ends & the more I struggled to get out, the more it seemed to trap me. Eventually got through it with just a couple of hints from Mark's solve. Great puzzle.

[piarittersporn]

A really beautiful puzzle, which I solved with great pleasure.

[henrymarkson]

I can't believe how quickly Mark saw the 1/5 in short equal sums line. I knew that was the key in the endgame I was staring at it but it took me ages to see it.

[brucedwuk]

These videos are just wonderful. It’s so encouraging when you are stumbling around in a bit of a haze, putting in some pencil marks and making some reasonable deductions to realise that you are following exactly the same trail of breadcrumbs that Mark has flown by two hours previously. It’s terrific being able to see where those key breakthroughs are - like the ending where he spotted the 15 clash - and pausing the video and moving forward on your own with that extra flicker of light. It makes these a perfect combination of learning and entertainment. Thank you both so much. First ever comment here!

[georgethackston]

I needed this one after the last few. I'm good with sums, but absolutely terrible at shading regions or groupings of cells. This one was really nice. CTC, thanks for all the joyful frustration and a belated congratulations on 500K!

[samplename]

Wow i went about the disambiguating line at the end in a very overcomplicated way, well worth watching the video to remind myself of all the possible tricks. Thanks

Diagonal sudoku start: two-digit line segments can't be the same in all 4 places creating a Shroedinger central cell. So many nice ways to eliminate 16+!

[Coyotek]

Took me two sessions and a total time of 38:06, but I finally figured out a way through to the end.

Nice puzzle!

[glum_hippo]

Very nice puzzle with some marvelous logic indeed. Thank you for featuring this gem! While I love the giant, spectacular puzzles with special tricks to solve them, it's always more than welcome to see a nice intricate exemplar such as this one with a quieter brilliance.

[aere]

I agree that the 98 or 97 duplication onto the 3 cell blue line is easier to break-in. Later on in the puzzle, I think the corner boxes can be disambiguated easily by looking at the 12 or 34 pair across the diagonals and seeing how they got forced. Great puzzle, I liked the logic.

[victorolosaurus]

this might have been the nicest "final stretch" in any puzzle here