Lean 4 Formal Mathematics Engineer at Mercor

Lean 4 Formal Mathematics Engineer | $90-110/hr | Part-time | Remote

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 researchers judge whether a model's proof actually proves the right thing. This is a W-2 position with Cincinnatus LLC (or an appropriate international entity), placing you within the lab's extended workforce.

What the work involves

• 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, checking that 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.

Who it's for

• Hands-on experience writing formal proofs in Lean 4, e.g. mathlib contributions, a formalization project, a Lean library or tool, or autoformalization work.
• Comfort with mathlib, Lean 4 tactics, and 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 that checks.
• Clear written communication to explain proof strategy and formalization choices.

Nice to have: experience with other proof assistants or dependently typed languages (Coq/Rocq, Isabelle, Agda, Haskell), Lean metaprogramming, or AI-for-math work such as LLM provers, Lean agent environments, or benchmarks like miniF2F, ProofNet or PutnamBench. You don't need all of these to apply.

Pay and schedule

$90-110/hr, part-time with at least 20 hours per week during weekdays, with the option to increase to up to 40 hours per week.

Cincinnatus LLC is an equal opportunity employer and does not discriminate on any legally protected characteristic.