Lean Engineer, Formal Mathematics (Lean 4, Mathlib, Theorem Proving) (remote)
About the role
Help a leading AI lab teach its models to write real, machine-checked mathematics in Lean. 1\. Overview A leading AI lab is looking for Lean engineers, formal mathematicians and proof engineers to help its AI models state and prove mathematics correctly. You'll write and review Lean 4 proofs, turn informal math into precise formal statements, and help the lab's researchers judge whether a model's proof is not just accepted by the checker but actually proves the right thing. If you enjoy writing Lean, know your way around mathlib, and can explain why a formalization is faithful or subtly wrong, this role is for you. This is a part-time commitment of at least 20 hours per week, with the option to increase to up to 40 hours per week. This is a W-2 employment position with Cincinnatus LLC (or appropriate international entity), with the opportunity to be placed at a leading AI lab as part of their extended workforce. 2\. Key Responsibilities - Write correct, idiomatic Lean 4 statements and proofs that compile against current mathlib, across areas such as algebra, analysis, number theory, combinatorics and logic. - Formalize natural-language mathematics, from competition problems and textbook results to research-level lemmas, paying close attention to whether the formal statement matches the original. - Review AI-generated Lean statements and proofs, find where they fail or prove the wrong thing, and give clear, specific written feedback. - Help define guidelines and rubrics for proof quality, statement fidelity and mathlib conventions. - Collaborate with other Lean engineers and the lab's researchers to keep standards consistent and keep raising the quality bar. 3\. Core Qualifications - Hands-on experience writing formal proofs in Lean 4, for example mathlib contributions, a formalization project, a Lean library or tool, or autoformalization work. - Comfort with mathlib and Lean 4 tactics, and with finding and using the right lemmas. - A strong background in proof-based mathematics, theoretical computer science or logic, through a degree or a research record. - The ability to turn a written statement and proof into a correct formal statement and a proof that checks. - Ability to engage reliably for at least 20 hours/week during weekdays. - Clear written communication and the ability to explain proof strategy and formalization choices precisely. Nice to have: experience with other proof assistants ... Pay: $90 to $110 an hour (USD). Remote contract work through Mercor. Apply on Mercor, upload your CV and complete a short AI interview.