In the words of the @0xPolygon Founder, @sandeepnailwal, he defined the Pessimistic proof as a ZK security solution that makes sure no chain can withdraw more from the shared bridge than they deposited.

Describing further, Pessimistic proof is simply a zk-security for cross-chains interoperability, also a cryptographic solution integrated into the Agglayer to treat all chains as unreliable and will strictly investigate them. In other words:

The Pessimistic proof is a protective and defensive coverage over transactions in the Agglayer across diverse cross-chains, with smooth communication and interaction between those chains.

With this protocol live on the Mainnet, it prepares the framework for the Agglayer to operate on numerous stacks, thereby ensuring safety for cross-chains transactions.

The proofs on the Agglayer V0.2 brings different chains together and unifies them, this upgrade brings two specific features into the system:

1. Flexibility: connections of chains of different security models

2. Safety: provides safety for cross-chains interoperability.

How the Pessimistic proofs works.

- It uses a unified bridge in making the #Agglayer a decentralized protocol that scales blockchain s by unifying liquidity, users and states.

- It provides the cryptographic assurance that allows chains to connect to a shared bridges without trust.

- It allows users move assets from chain A to chain B without an intermediary, portraying transparency in the Agglayer

- The Pessimistic proof always makes sure that no chain are manipulating deposits to other chains.

- The Agglayer forms the Pessimistic proofs by working with three important information:

1. Chains update correctly

2. Chains performs their internal accounting correctly i.e. does not try to withdraw tokens it does not have.

3. All chains have performed correct internal accounting.

Benefits to the Agglayer

- The Agglayer is able to compute how transactions are made between different chains, this is to prevent any boycott in the system.

- Makes the Agglayer safe, smart and secure for transactions.

- Fast and seamless communication between chains

- Adequate interoperability

- Scalability and liquidity

- No loss of message from one chain to the other.

- The Agglayer becomes accessible to other chains and not just those on the Polygon CDK.

This upgrade is an important prerequisite for the Agglayer to enter into it's next phase of upgrade.

Read more about the Agglayer Upgrade via the blog post:

https://polygon.technology/blog/major-development-upgrade-for-a-multistack-future-pessimistic-proofs-live-on-agglayer-mainnet