Developed an axiomatisation for interior mutability in the Creusot verifier, focusing on introducing predicates for Rust’s std::cell::Cell to enhance formal verification of code using interior mutability patterns. This work, delivered in the creusot-rs/creusot repository, enabled predicate-based reasoning that improves the precision of verification and reduces false positives when analyzing Rust programs. The approach emphasized formal methods and verification techniques, laying a foundation for broader support of interior mutability in Creusot. All contributions were traceable through repository commit history, supporting future audits and incremental improvements. No bug fixes were recorded, with efforts concentrated on feature development and verification.