Lean 4 Proof Engineer for AI Math & Formalization

AI Trainer Jobs; United States; Remote; USD 96,000 - 165,000; Full time

Benefits offered by this job

W-2 employment

Placement at leading AI lab

Job summary

Cincinnatus LLC is seeking Lean engineers, formal mathematicians and proof engineers to help its AI-lab client state and prove mathematics in Lean 4. This part-time W-2 role offers 20–40 hours per week and a path to more work.

You will write and review Lean proofs, formalize informal math, and help ensure proofs are faithful and correct. Placement at a leading AI lab as part of the extended workforce is available, with opportunities to shape formalization guidelines and collaborate with

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 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.

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.

Skills

Lean 4

Formal proof

Mathlib

Proof engineering

Strong communication

Education

Bachelor's or higher in Mathematics/CS

Tools

Lean 4

mathlib

Job description

Cincinnatus LLC is seeking Lean engineers, formal mathematicians and proof engineers to help its AI-lab client state and prove mathematics in Lean 4. This part-time W-2 role offers 20–40 hours per week and a path to more work.

You will write and review Lean proofs, formalize informal math, and help ensure proofs are faithful and correct. Placement at a leading AI lab as part of the extended workforce is available, with opportunities to shape formalization guidelines and collaborate with