The Bifrost EOS interoperable bridge is a substrate-developed project that combines SPV client and multi-signature mechanisms to build a secure, flexible, and scalable cross-chain without modifying the core functionality of the parent chain. We also envisioned a version in which the parent and side chains are SPV clients of each other. This version is more distributed and safer, but it is costly and difficult to implement. The current approach not only allows the user's assets to be chained, but also the staking benefits of the parent chain. In the future, it can also support any operation across the chain for true interoperability.