yes and bitcoin builds on top of that, I believe the white paper may cite that effort, it cites W Dai’s b-money paper from 1998
The bitcoin white paper specifies that this is a solution without a trusted intermediary
the first line of the abstract entails not using a financial institution
I agree that ‘unsolved’ was inaccurate, I try to also say bitcoin 2008 is one implementation and essentially all distributed ledgers are following this branch of solution
additional solutions remain evasive
The likes of Wei Dai, David Chaum, and Stephan Brands had working anonymous "digital cash" cryptosystems solving the double spending problem within a federated banking model in the late 80s and early 90s
https://groups.csail.mit.edu/mac/classes/6.805/articles/mone...