Alex Keizer
Applied Scientist at Amazon Web Services (AWS)
Cambridge, England, United Kingdom
Summary
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Rockstar🎓
Top SchoolAlex Keizer is an applied scientist and PhD candidate at the University of Cambridge with eight years of software engineering experience spanning formal methods, backend systems, and web development. Currently at AWS, he built and optimized a symbolic ARM simulator in Lean capable of symbolically executing production cryptographic routines, reflecting a rare blend of theorem-proving expertise and practical systems optimization. His open-source contributions to the prominent Lean 4 theorem prover—particularly the BitVec module and bitvector theorems—demonstrate deep formal-verification skills that inform his work on symbolic simulation and low-level correctness. Previously he delivered backend systems using PHP, Yii, and relational databases across multiple startups, bringing hands-on full-stack experience to research-grade engineering problems. Fluent across formal logic, compiler-level reasoning, and production backends, he combines rigorous academic training with pragmatic implementation focus.
8 years of coding experience
Doctor of Philosophy - PhD Informatica, Doctor of Philosophy - PhD Informatica at The University of EdinburghDoctor of Philosophy - PhD Computer Science, Doctor of Philosophy - PhD Computer Science at University of CambridgeBachelor of Science - BS Informatica, Bachelor of Science - BS Informatica at Leiden UniversityMaster Logic, Master Logic at University of Amsterdam
Github Skills (8)
theorem-proving10
leanback10
data-structure9
back-end-development9
algorithm9
data-structures9
algorithms9
formal-verification8
Programming languages (10)
Github contributions (5)
leanprover/lean4
Jul 2023 - Mar 2025
Lean 4 programming language and theorem prover
Role in this project:
Back-end Developer
Back-end DeveloperContributions:83 reviews, 30 PRs, 191 comments in 1 year 8 months
Contributions summary:Alex primarily contributed to the Lean 4 programming language and theorem prover, focusing on the `BitVec` module. Their work involved implementing and refining features related to bitvector operations, including multiplication, concatenation, and bitwise operations. They added and refined theorems about the behavior of unsigned and signed bitvector inequalities, which are crucial for bit-blasting, alongside related work on `Fin` and `Nat` operations. Moreover, the user implemented and refined the `toInt` method.
dependent-typeshomotopy-type-theoryprovertheoremtheorem-prover
alexkeizer/LNSym
Aug 2024 - Sep 2024
Contributions:2 PRs, 215 pushes, 37 branches in 1 month
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