Lean Engineer for Formal Math & Lean 4 Proofs

Mercor; Greater London; On-site; GBP 55,000 - 83,000; Part time

Job summary

Cincinnatus LLC is seeking Lean engineers and proof engineers to help its AI lab formalize mathematics in Lean 4. You will write and review Lean proofs, translate informal math into precise formal statements, and judge whether proofs actually verify the right results.

The role is part-time (at least 20 hours/week, up to 40) with potential for extension or placement at a leading AI lab as part of the extended workforce. Previous Lean 4 and mathlib experience is essential.

Qualifications

• Hands-on experience writing formal proofs in Lean 4 with mathlib.
• Ability to turn informal statements into formal, checkable proofs.
• Experience with Lean 4 tactics and mathlib lemmas.
• Strong background in proof-based mathematics or logic.

Responsibilities

• Write correct Lean 4 statements and proofs that compile against mathlib.
• Formalize natural-language mathematics into precise formal statements.
• Review AI-generated Lean statements and provide clear feedback.
• Help define guidelines for proof quality and conventions.
• Collaborate with Lean engineers and researchers to raise standards.

Skills

Lean 4

mathlib

Formal proofs

Proof strategies

Clear communication

Education

Degree in mathematics / CS / logic

Tools

Lean libraries

Math libraries

Job description

Cincinnatus LLC is seeking Lean engineers and proof engineers to help its AI lab formalize mathematics in Lean 4. You will write and review Lean proofs, translate informal math into precise formal statements, and judge whether proofs actually verify the right results.

The role is part-time (at least 20 hours/week, up to 40) with potential for extension or placement at a leading AI lab as part of the extended workforce. Previous Lean 4 and mathlib experience is essential.