Proof-of-stake does not solve the Byzantine General's Problem. Therefore, it does not provide decentralized consensus. This effectively "unsolves" that which PoW solved.

This paper is not proof (https://eprint.iacr.org/2016/889.pdf), they assume away the Byzantine Generals problem.

Proof-of-stake does not solve the Byzantine General's Problem. Therefore, it does not provide decentralized consensus.

PoW is the only known solution: https://gist.github.com/oleganza/8cc921e48f396515c6d6

This paper attempts to provide proof but fails (https://eprint.iacr.org/2016/889.pdf), they effectively assume away the Bizantine Generals Problem.