# Week 16 Update

Hi there, for this week I completed their implementation and spec tests for the [ssz-z library ](https://github.com/ChainSafe/ssz-z)
- [Progressive Bitlist](https://eips.ethereum.org/EIPS/eip-7916)
- [Progressive Containers](https://eips.ethereum.org/EIPS/eip-7495)

I am waiting for the updated consensus spec tests since `v1.6.0-beta.0` still contains the buggy data.

### What are Progressive Containers anyways?
SSZ containers are frequently versioned, for example across fork boundaries. Lets say a field is removed or replaced with one of a different type, the shape of the underlying Merkle tree changes, breaking verifiers of Merkle proofs for these containers. Deploying a new verifier is very troublesome. Progressive containers address these shortcomings by:
- Using the progressive Merkle tree structure to progressively grow to the actual field count with minimal overhead, ensuring provers remain valid as the field count changes.
- Assigning stable gindices for each field across all versions by allowing gaps in the Merkle tree where a field is absent.
- Serializing in a compact form where absent fields do not consume space.

## Return of ERA

I finally got a review on my [era pr](https://github.com/ChainSafe/lodestar/pull/8035) and its a small refactor catering to the needs of lodestar.

## Work for the next week
- Since only [Compatible Union](https://eips.ethereum.org/EIPS/eip-8016) is left as of Progressive Types, i will be reviewing [this pr](https://github.com/ethereum/consensus-specs/pull/4581).
- Get my pr merged and work on the db integration