Worldwide
Lean Engineer, Formal Mathematics (Lean 4, Mathlib, Theorem Proving)
$90 – $110 /hr
Compensation
Part-Time
Employment
Senior Level
Experience
Oct 13, 2026
Posted
About this opportunity
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.
Key responsibilities
- 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.
Benefits & perks
- Employment Details:
- W-2 employment position with Cincinnatus LLC (or appropriate international entity), placed at a leading AI lab.
- Part-time — at least 20 hours/week, option to increase to 40 hours/week.
- Fully remote.
- Offer Details:
- Pay rate: $90 – $110/hour.
- Referral bonus: up to $1,760 per successful referral.
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Lean Engineer, Formal Mathematics (Lean 4, Mathlib, Theorem Proving)
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Title: Lean Engineer, Formal Mathematics (Lean 4, Mathlib, Theorem Proving)
Categories: AI Training, AI Evaluation, Formal Methods
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