Portrait of a flying fish

If, like me dearest reader, you are interested in sudoku solving techniques, then perhaps this is an interesting link to a youtube video.

• https://www.youtube.com/watch?v=n2No8hU2OwI

If you found that video interesting, then perhaps this is an interesting picture.  [Someone going by the pseudonym shye is responsible for this puzzle, and it even has a name.  Imagine that, dearest reader: a sudoku with a name!  Rather grandly, this one is called "Valtari"]

If you found that picture interesting, then perhaps these are some interesting words.

• Add rows 1, 3, 5, 7, 9 together with box 5 (in blue, with double weights in R5C4 and R5C6).
• Subtract Columns 3, 5, 7 (in red).
• The blue cells, considered with multiplicity, have the same contents as the red cells plus 3 extra copies of the digits 1-9.
• In the double-weighted blue cells, the only possibilities are 2, 3 and 4.
• There are already exactly two each of 2, 3 and 4 appearing as given digits in the single-weighted blue cells.
• This means that whichever two of the three digits ends up in the double-weighted blue cells will end up bring the multiplicity of both of those digits up to 4 within the blue cells.
• This means that the two empty red cells have the same contents as the two empty double-weighted blue cells.
• It also means that those two digits cannot appear again in any other blue cell.
• More on this to come I'm sure, following this good work by Philip Newman: https://docs.google.com/document/d/1Y7m2tTUDmUTj3BZ0w5viNuQlaiBVv9kmYksSLrm_XLE/edit

UPDATE: as far as I can tell, there is no need to add Box 5 to the equation here - this makes the intersections slightly simpler (no need for double-weights any more) - but it does make it harder to identify where you are supposed to be looking.

If you didn't find that interesting, then I'll leave you with some whimsical musings.  I always thought that an obscure and difficult sudoku solving technique going by the name Exocet was named for a powerful missile that could bust open the hardest of puzzles.  Cela a plus de sens en français.

Concord and Discord

I was pleased to receive a couple of messages on discord yesterday by virtue of sharing a server - namely the cracking the cryptic server.  Unfortunately I can't reply to any messages any more as I've decided it's for the best for me to leave that server, perhaps permanently.

The first message was from Philip Newman, letting me know about a document he's been working on.

https://docs.google.com/document/d/1Y7m2tTUDmUTj3BZ0w5viNuQlaiBVv9kmYksSLrm_XLE/edit

This is, in fairness, an acquired taste.  It takes what was to me an impenetrable concept of sudoku solving techniques (Exocets), and relates them to a slightly less impenetrable concept of sudoku solving technique, namely "SET".  

As an aside, I don't think endless jargon, neologisms, portmanteaus, puns and acronyms is always very helpful when it comes to the dispersal of knowledge and understanding.  I should say that SET stands for "set equivalence theory", which is what has emerged following some of the discussions and posts on this blog (I still don't like that word even after all these years!) in autumn 2020.  I'd previously referred to it vaguely as intersection theory and will probably continue to do so in the future as well, in case that causes any confusion.

Anyhow, whilst I might not love the words, I do find the underlying conepts fascinating.  if you enjoyed said posts and discussions from last autumn then I think you'll enjoy Philip's document.  In particular, it seems to move the discussion on to more complicated and extended equivalent sets/intersections, and in particular more complicated interactions inside individual instances of them.  The way in which seemingly unrelated cells become strongly related turns out to be far more subtle than we really touched on previously.

Hopefully the last section implies this isn't going to be the final word on the matter either!  Maybe I'll take the time to add my own musings on Philip's work if I can muster up time and/or motivation.

The second message I received was from someone who had read one of my earlier blog (ugh) posts where I had previously mentioned that I wasn't having a great time on either the Puzzler's Club or the Cracking the Cryptic discord servers.  

https://tcollyer.blogspot.com/2020/09/348-doppelblock.html 

I tried to reply privately to that message, but it turns out that having left the server I can't send the message.  So on the off chance that person is also reading this, let me reply in slightly less specific terms: thank you for your message, it was very kind of you to think of me and there was certainly no need to apologise on anyone's behalf.  Plenty of people have a better time of it there than I do - I can only relate my own experience.  At times (not all the time) it can feel very cliquey, hierarchical and beset by an unpleasant group-think of what is and isn't the best way to think about things.  

I particularly appreciate that is by no means reflective of all the members of the server, but it is reflective of enough it for me to conclude that it doesn't really work for me right now.