Diabolical sudoku: Some more tips

Simon talks through his solve of The Daily Telegraph's Diabolical Sudoku from 15 June 2018.
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[@kristofersokk1580]

The 8 logic at 3:42 actually works. The r8c9 8 would force r9c5 to be an 8, which locks 8 to r45c6, which using uniqueness with the ones removes all options for an 8 in box 6. That allows r4c9 to be an eight, after which you can put 8 to r5c6 which solves the ones.

[@samcappleman-lynes6914]

Both trials that eliminate, respectively, an 8 and a 9 can be equivalently derived using a pattern which crops up rather often in these puzzles which are just over the cusp of difficulty - a Sashimi X-Wing. The first is on the 8s in columns 5 and 9 - it is available as soon as the 8 has been placed in r6c1. The second is on 4s in columns 2 and 9 - it is available once the 6 has gone into r1c2. Spotting both of these leaves just the Unique Rectangle before an easy remainder of the solve. Certainly a good weapon to have in your arsenal - worth a quick check when you notice that a digit is constrained to only two places in a row or column.

[@jerryabbanat9452]

Thanks Simon for another great video

[@titushui]

Patterns found- Skyscraper of 8(r5c67 and r9c57 to eliminate 8 in r4c5 and r8c6), Unique Rectangle of Type 4 of 1-8 for multiple solutions and also Empty Rectangle case of 9 at the end.

[@kimstockdale632]

Wonderful demo on how to extend beyond "Snyder notation" strategy! Especially the mental trial & errors (for 8s at 5:00, and 9s at 14:15). Is that trial & error method what you mean by "bifurcation?" Also at 7:20 your discussion of possible dual solutions that eliminates two possible cells in column 6, else the puzzle would not have a unique solution.

[@stalbrmusic498]

I had to watch this, very good! Could you maybe make a video where you explain what you are looking for when that "simple" technique you use won't give you any more numbers? Would be very nice!

[@stalbrmusic498]

ok that thing on 6:30 for example was already quite helpful;)

[@alfredotrotta5915]

Hi Simon, which software are you using in this video? I'm looking for one that can help following chains. Can you advice? Thanks a lot

[@cpgautam172]

Wait isn't the 8 in the bottom middle block wrongly placed?

[@moshehim1000]

Hi, I don't understand what you did 4:40 onwards. 1. You say "little eights down here" and notate cells r8c4 and r9c5. I'll grant you 19c5, but hoe do you recon r8c4? There's already an 8 in r1c4 which precludes all other cells in c4 from being an 8! 2. I figured there could be an 8 in r8c6, but you didn't notate it at all. 3. They you go into some convoluted chain of eights to prove r4c5 is not an 8 and therefore the only possible place for an 8 in c5 is in r9. But how did you know to specifically test one of the pair of eights in c5 and not any other pair anywhere else? For example, there are only two positions to put sixes in column 7, there are only two positions to put fives in row 7, and only two positions to put sevens, also in the same row. Only two positions to out ones in row 2, as well as only tow positions to put twos in that row. Yet you never test any of them. Why not? I've been trying your method of marking sets of two cells with the same digit, but I always reach a stage when that stops working, and I can't find any pattern like hidden triples or x-wing with or without fins, so I try putting the sudoku in a solver that's pretty good in giving you hints on how to continue, but I get a message there are no hints available. So then I try a second solver, which first fills all of the pencil marks everywhere - something you advocate against, then it commences to eliminate notations one after the other using a similar technic, only exponentially more convoluted, and I never understand how I was suppose to spot that with a naked eye and a mortal brain - with or without all those markings. So I'd appreciate if you could share which clue prompted you to try that particular pair of eights specifically and not any other pair. Thanks.

[@milkom2021]

What other pairs? He marked all the remaining eights and found a Skyscraper pattern in columns 5 and 9

[@dave84346]

All to fast doesn't explain slowly enough how he got each move great video showing his skill but not for teaching just showing off