Plasma = Layer2 (OPU, ZkR)
In other words, the problem was that it was possible to justify fraudulent assets by taking advantage of the worst-case data accessibility issue and winning the Exit Game. This issue was resolved by introducing a mechanism to reject transactions that are mistakenly included on-chain for L2 transactions, thus eliminating the data accessibility problem. The later Exit Game was addressed by using zero-knowledge proofs to reject updates to fraudulent Merkle Roots or by providing proof of fraud within 7 days (fraud proof). The former is called zkRollup, and the latter is called Optimistic Rollup. Rollup refers to the method mentioned above. Layer2 aims to reduce transaction fees and improve transactions on Ethereum. Layer2, as the name suggests, refers to the second layer. The first layer is the Ethereum blockchain. Layer2 is built on top of the Ethereum blockchain (first layer). The idea is that not all processes need to be done on Ethereum (on-chain) because it is challenging, but some processes can be done off-chain.
Types of Layer2:
Layer2 is a method proposed to address the scaling problem of Ethereum's Main Chain. It involves using a separate Layer2 chain for calculations and data storage to solve the scaling problem.
In the short term, I believe that Optimism and Arbitrum, which adopt Optimistic Rollup, will be widely used. The reason is that they are developer-friendly and allow the use of EVM (Ethereum Virtual Machine) code written in Solidity. However, in the long term, I think Zk-Rollup will prevail. The reason is that The disadvantage of Optimistic Rollup is that withdrawals cannot be made for 7 days, which is resolved by ZK-Rollup. zkSync is experimenting with Zk-Rollup.