Contributed to the leanprover-community/batteries repository by implementing a new DecidableEq instance for the Except type, enhancing type safety and decision-making in Lean programming. This feature leveraged Lean’s type-class derivation mechanisms and functional programming principles to strengthen compile-time guarantees for error-handling code paths. The work reduced the risk of runtime ambiguity and improved reliability for downstream users working with the Except type. Collaboration was emphasized through co-authorship, reflecting open-source development practices. The contribution demonstrated proficiency in Lean, type theory, and cross-repository maintenance, focusing on improving the robustness and maintainability of the codebase without introducing new bug fixes during the period.