Roman Kvasnytskyi refactored the LSeries_congr lemma in the leanprover-community/mathlib4 repository, focusing on improving code ergonomics and maintainability. By moving the evaluation argument s to the last position, Roman enhanced readability and enabled easier partial application, aligning the lemma’s structure with related components in the codebase. This change streamlined downstream formalizations, reducing cognitive load for future contributors and facilitating smoother collaboration. The work demonstrated proficiency in Lean, code refactoring, and formal verification, addressing the need for standardized argument order in mathematical proofs. Over the month, Roman delivered one feature, contributing depth and clarity to the mathlib4 pipeline.