Lean 4 proves LLM COBOL translations match originals

Researchers demonstrate that LLM-translated whole COBOL programs into Rust and Java can be formally proved in Lean 4 to behave identically to the originals on all admissible inputs. Testing revealed that 35% of initial translations differed from the original semantics, but Lean's kernel successfully checked proofs for all eight standalone batch programs from AWS CardDemo without missing any differences. The generated statements ensure program equivalence for Rust and refinements with partial correctness for Java. Open article →