Worked on the leanprover-community/batteries repository, focusing on improving the robustness of lambda handling within common tactics. Addressed a bug related to the misuse of implicit lambdas in the by_contra and absurd tactics by explicitly managing lambda expressions, which helped ensure deterministic and predictable proof construction. The approach involved a targeted refactor in Lean, maintaining code quality with minimal changes and clear commit documentation. Leveraged formal verification and theorem proving skills to enhance the reliability of proof tactics. The work contributed to the overall stability of the Batteries library, emphasizing careful code maintenance and precise handling of Lean’s language features.