Part-Time Lean Engineer: Formal Math & Lean 4 Proofs

Mercor; San Francisco (CA); On-site; USD 96,000 - 152,000; Part time

Benefits offered by this job

W-2 employment

Placement at leading AI lab

Flexible 20–40 hours/week

Job summary

Cincinnatus LLC is seeking Lean engineers and formal mathematicians to help an AI lab state and prove mathematics in Lean 4. You will write and review proofs, formalize informal math, and assess whether proofs align with the intended results.

The role is part-time (at least 20 hours per week) with potential to increase to 40 hours, and involves W-2 employment through the employer of record and placement at a leading AI lab as part of the extended workforce.

Qualifications

• Hands-on experience writing formal proofs in Lean 4, for example mathlib contributions or Lean projects.
• 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.

Responsibilities

• Write correct, idiomatic Lean 4 statements and proofs that compile against current mathlib.
• Formalize natural-language mathematics, from problems to lemmas, ensuring the formal statement matches the original.
• Review AI-generated Lean statements and proofs, identify failures, and provide precise feedback.
• Help define guidelines and rubrics for proof quality and mathlib conventions.
• Collaborate with Lean engineers and researchers to maintain high standards.

Skills

Lean 4 proof writing

mathlib familiarity

formalization experience

proof strategy explanation

20 hours/week availability

clear written communication

Education

Degree in math/CS or research in logic

Tools

Lean 4

mathlib

Coq/Rocq/Isabelle

Lean metaprogramming

Job description

Cincinnatus LLC is seeking Lean engineers and formal mathematicians to help an AI lab state and prove mathematics in Lean 4. You will write and review proofs, formalize informal math, and assess whether proofs align with the intended results.

The role is part-time (at least 20 hours per week) with potential to increase to 40 hours, and involves W-2 employment through the employer of record and placement at a leading AI lab as part of the extended workforce.