Giacomo Grevink contributed to the dhyan-aranha/FormalBook repository by refactoring the valuation lemma to leverage Zorn’s Lemma, introducing a new set of subrings without 1/2, and reorganizing related proofs to improve mathematical rigor and extensibility. Working in Lean, Giacomo enhanced the maintainability of formal proofs by adding explanatory comments and cleaning up existing arguments. He also addressed documentation accuracy by correcting a contributor’s name in Chapter_22.lean. His work combined formal verification, mathematical proof development, and documentation, resulting in deeper, more robust formalizations and clearer code structure, supporting future extensions and ensuring the repository’s ongoing reliability and clarity.