TL;DR

1) Since both layer 2 and layer 3 theoretically rely on the mainnet for settlement, a common assumption is that layer 3 first compresses the data and then submits it to layer 2 for secondary compression, essentially layering a Rollup on top of another Rollup. This approach has been criticized and questioned because if one were to imagine layer 4 and layer 5 using a similar architecture, it would lead to a dead end, as data cannot be compressed indefinitely.

2) In reality, the interaction between layer 3 and layer 2 might not necessarily involve compressing and then re-compressing. In the layer 3 strategies planned by multiple layer 2 stacks such as Arbitrum and zkSync, layer 3 is defined as a specific application chain. It will have a high degree of autonomy in aspects like consensus mechanisms, gas fee choices, and economic models. However, autonomy does not mean complete independence, as the underlying architecture is likely constrained by the foundational infrastructure built for layer 2, such as sharing key components like Sequencers and Provers with the layer 2 chain.

This means that transactions on layer 3 are directly processed by the layer 2’s Sequencer and submitted to the mainnet for final state confirmation. Layer 2 takes on more of a role in enabling interoperability functions among multiple layer 3 chains, where the so-called “settlement layer” is merely for data packaging and not the final settlement in the true sense. Transactions on layer 3 also need to queue on layer 2 for packaging, making it sensible to treat the layer 3 application chain as a special type of Sequencer channel.

3) Assuming that layer 3 operates purely as a nesting of chains within chains naturally limits scalability, but this practice is just a theoretical assumption. If layer 2 and layer 3 share critical components like Sequencers and Provers, there are many ways to enable horizontal scaling of layer 3 chains, especially when inter-chain interoperability is enhanced.

1. As mentioned by the founder of zkSync, @gluk64, using ZK technology as a foundation for interoperability between multiple blockchains is feasible because ZK technology enables two counterparties to verify the authenticity of information without revealing the details. When assets are transferred from Layer 3 to Layer 2, this can be seamlessly accomplished via a ZK bridge, enabling atomic asset transfers between chains without the need for additional inter-chain consensus or other processes.

ZK technology-enhanced bridging enables foundational support for the multi-chain expansion of Layer 3 because, regardless of how many Layer 3s are deployed, they directly settle with Layer 2 via ZK Proofs, which does not affect the relationship between Layer 2 and the mainnet;

1. As described by the founder of Eigenlayer, @sreeramkannan, having the AVS active nodes of Eigenlayer coordinate consensus across different blockchains essentially involves the same set of nodes participating in consensus building across multiple chains. By implementing a reward and penalty (Slash) mechanism for AVS, it is theoretically possible to reduce the likelihood of nodes acting maliciously. If nodes approve the transfer of assets from Layer 3 to Layer 2 and there is misconduct, they would be subject to slashing.

This type of reward and punishment economic mechanism can also be applied to trust issues in a multi-chain environment. Although it cannot achieve the same level of trust as ZK technology, it can roughly create a trustworthy environment based on an economic model.

4) @VitalikButerin, in response to discussions that often carry inherent biases, reiterated his view that Layer 3 should not be simplistically seen as just a stack or extension of Layer 2, as this does not necessarily bring effective scalability. Since Layer 3 depends on Layer 2 as its infrastructure and Layer 2 itself cannot expand indefinitely, the same is true for Layer 3. However, in certain specific scenarios, such as privacy, specific privacy-oriented Layer 3 applications can address some of the transactional preferences for privacy.

In conclusion, Layer 3 represents a highly customizable feature with potential for tailored expansion. From my perspective, the expansion of Layer 3 should be based on application-specific needs and developed in a custom-tailored manner, unlike a one-size-fits-all development paradigm, which is not feasible in a multi-chain direction for Layer 3 applications.

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