[rocqua]

You can replace PoW by a simple signatures, or a quorum of signatures. This is quite centralized, but still write-once.

In any case, with a 'hash-linked-chain-of-blocks' attempted forks are really easy to prove.

[ruiquelhas]

I get that, but there are no guarantees it is write-once, because it might happen that the "quorum of signatures" changes their mind.