Johannes Hölzl
Formal Verification Engineer
Munich, Bavaria, Germany
Summary
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Rockstar🎓
Top SchoolJohannes Hölzl is a Formal Verification Engineer based in Munich with 26 years of experience building rigorous, provable software and mathematical libraries. He holds advanced degrees from TU München and has a strong academic pedigree with postdoctoral research at CMU and Vrije Universiteit Amsterdam before joining Apple in 2019. Johannes is an active contributor to the Lean theorem prover ecosystem (Lean 3 and Lean 4), where he implemented core algebraic structures, lattice instances, and foundational real-analysis formalisms that underpin mechanized proofs. His work blends deep theoretical expertise with practical engineering—refactoring core libraries, fixing subtle bugs, and improving transfer methods to make formal reasoning more maintainable. Notably, he pairs long-term research experience with hands-on tool-building for verification, from automated hardware test environments to formal proof assistants.
26 years of coding experience
8 years of employment as a software developer
Diplom, Informatik, Diplom, Informatik at Technische Universität München / TU MunichDr. rer. nat, Informatik, Dr. rer. nat, Informatik at Technische Universität München
German, English
Stackoverflow
1reputation
0reached
0answers
0questions
Github Skills (13)
topology10
slim10
proofs10
data-structures10
theorem-proving10
proof10
t410
leanback10
algebra10
data-structure10
ordered-set9
ordered9
formal-verification9
Programming languages (6)
Github contributions (5)
leanprover-community/mathlib3
Jul 2017 - Sep 2019
Lean 3's obsolete mathematical components library: please use mathlib4
Role in this project:
Back-end Developer
Back-end DeveloperContributions:374 commits, 257 PRs, 404 pushes in 2 years 1 month
Contributions summary:Johannes implemented foundational elements of real analysis, focusing on defining real numbers as a complete, linear ordered field. The code changes primarily involve contributions to a mathematical components library written in the Lean 3 language, likely for formal proofs and theorem proving. The changes appear to be related to the development of a topological framework for mathematical structures, focusing on filters and metric spaces. The user's work also includes modifications involving topological and measurable spaces.
maththeorem-provingcomponents-librarymathematicsjavascript
leanprover/lean3
Jan 2016 - Aug 2017
Lean Theorem Prover
Role in this project:Back-end Developer
Back-end DeveloperContributions:45 commits, 22 PRs, 82 comments in 1 year 7 months
Contributions summary:Johannes contributed to the Lean Theorem Prover by implementing and refactoring core algebraic structures. They added functionalities such as Galois connections, lattice instances for propositions, functions, and sets. The user also refactored theorem names and fixed bugs within the algebraic libraries.
provertheoremtheorem-provertheorem-provinglean
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