In the merkle tree committment example, I don't think it allows identifiying e.g. a fraudulent rollback just from looking at the hash. If you wanted to identif

In the merkle tree committment example, I don't think it allows identifiying e.g. a fraudulent rollback just from looking at the hash. If you wanted to identify a fraudulent rollback, I think you had to constantly replicate all transitions and recompute the on-chain merkle hash. If you found discrepancies in the on-chain hash and yours, it'd mean that either node ran out of synch for some unknown reason. Then, if e.g. other nodes too replicated your state, you may be able to conclude that the wrong-hash node had a (byzantine) fault etc. But I think that at least in the case of the Ethereum Plasma architecture, just committing a state aggregate in form of a hash wasn't enough because of some block withholding attack. From my understanding, hoytech's quadrable is just a chain committment. Similar to Plasma. Modern rollup architectures end up storing all transition state in Ethereum calldata state. This way proving fraudulent validation is possible and things become conceptually simpler as you can rely on the strong guarantees of e.g. data availability of the PoW chain.