---
# System prepended metadata

title: Migration proposal

---

# Migration proposal

## Issue
Insure that refutation procedures that overlap the transition block still work. For example if a hashing collision is discovered and the hash of the roll-ups is changed we need to insure that an invalid commitment cans still be refuted.

## Proposal

The problem window for the the above issue is verys short. Because of the ORU principle, after a certain number of blocks no refutation is possible anymore. Therefore we propose:
* fix a `rollup_rejection_delay_limit ` which is the number of blocks after which refutation is no longer possible.

* At the point of transition we measure the and, on the L1 chain, ignore all the commitments and preblocks that are newer than `rollup_rejection_delay_limit`. 

* in the roll-up keep a buffer of roughly the size of the `rollup_rejection_delay_limit` and, after the transition rewrite all the commitments in the buffer to l1 using the new protocol rules.

