What I saw on the web on 2022.12.21

[reblogarythm]

1. Free Idempotent Rigs and Monoids
   by John Carlos Baez
   https://johncarlosbaez.wordpress.com/2022/12/21/free-idempotent-rigs-and-monoids/
   a fun little algebraic question
   via rss
   
   
2. A Non-constructive Proof of the Four Colour Theorem.
   by D. M. Jackson and L. B. Richmond
   https://arxiv.org/pdf/2212.09835.pdf
   not yet peer reviewed, and i'm neither a graph theorist nor a generatingfunctionologist, so i can't tell if it's valid, but if it is, this is huge
   via reddit
   
   
3. Is Cb the same note as B?
   by Adam Neely
   https://www.youtube.com/watch?v=SZftrA-aCa4
   i'd say no, but i'm a just intonation bigot
   via rss
   
   
4. Track post-conference COVID infections
   by James Kirchner
   https://www.nature.com/articles/d41586-022-04469-8
   amazingly, being in a room with a bunch of people during an ærosol-transmitted pandemic can be hazardous to your health! and there's no covid umbrella over the cafeteria table?!?
   via FB