[tedk-42]

a) I hand my friend a $1 coin/note.

b) I socialise the transaction and have everyone try be the first to crack an algorithm that proves I've given my friend a cryptocoin worth $1

There's a community out there claiming one solves a bunch of problems the other had. You tell me...

[glitchc]

Stone money is where (a) looks like (b). It has been used successfully in the past, spanning multiple human generations of transactions:

https://en.wikipedia.org/wiki/Rai_stones