Preface The Bitcoin ecosystem cannot be built directly on Layer 1. The Bitcoin blockchain is not Turing-complete by design. Furthermore, Bitcoin's simple UTXO model and limited block space cannot handle complex data and computations. Therefore, the development of the Bitcoin ecosystem must rely on Layer 2, specifically a fully decentralized Bitcoin Layer 2. Over the past 15 years, Bitcoin has undergone several major upgrades, bringing numerous technological innovations, but these are oft...