Oh, wow, TIL that I studied with the American symbols in high school in Portugal, back in the 90s. I had no idea other symbols even existed.
Got on a sidetrack this morning and found this interesting little paper from 2004: "why proof of work doesn't work".
https://www.cl.cam.ac.uk/~rnc1/proofwork.pdf
(from a quick read of the conclusion, their argument doesn't appear that strong, but the basic idea is well known - attackers are prepared to spend a ton more to specialize, than ordinary users are, etc. etc.)
This paper might seem quaint to Bitcoiners who are convinced that PoW *does* work, but bear in mind: they are thinking of the spam problem specifically, and so their analysis could still be very relevant today, e.g. in the case of using PoW for systems like Tor or Lightning.
Interesting tidbit, the first author Ben Laurie is the guy, iirc, that invented "Lucre" an ecash system that is an early precursor of privacypass and cashu.
PoW without difficulty adjustment doesn't work.
The paper makes a bunch of assumptions that work for email but not Bitcoin mining. They assume that sending computer clients will remain slow while spammers can upgrade to fast computers.
In Bitcoin terms, that would be like saying you have to keep difficulty low because you have a lot of slower miners and that they couldn't participate otherwise. No, Bitcoin doesn't work like that, if a miner is slow and can't participate, tough luck, we don't compromise the Bitcoin network security because of that.
Try "clear cookies and site data". That fixed it for me.