Independent software engineering consultant with over a decade of professional experience. Previously worked at Acceleware, Microsoft Azure Compute, Microsoft Azure Networking, and Microsoft Quantum. BSc in Computer Science from the University of Calgary. From Canada, currently based out of Atlanta, GA, USA. TLA⁺ enthusiast!

Interested in hiring me for a contract? Contact me on LinkedIn or email consulting@disjunctive.llc. Work playing to my skills includes:

  • Formally specifying & model-checking your system with TLA⁺ [1] [2]
  • Formally proving the correctness of your system [1] [2]
  • Assisting in the design of your distributed system or protocol [1]
  • Analyzing your probabilistic system or protocol with PRISM [1]
  • Writing tricky distributed systems code for your system’s backend [1]
  • Validating your system’s implementation with model-based testing
  • Analyzing your access control system with the Z3 theorem prover [1] [2]
  • Writing a tree-sitter grammar for your domain-specific language [1]
  • Education in technical quantum computing concepts [1] [2] [3] [4]
  • General development work on formal methods tools themselves [1]

I have experience with C++, Java, C#, Rust, Golang, Python, and Kubernetes. See my full résumé here.

Email ahelwer@protonmail.com for personal correspondence. I’m always happy to answer questions about my interests, especially quantum computing!

Outside of work I’m an avid climber; find tales & photos of my adventures at outdoors.ahelwer.ca.

All content on this website is licensed under CC-BY-SA 4.0.

Writing a TLA⁺ tree-sitter grammar

My foray into free software

Writing a TLA⁺ tree-sitter grammar
2021 saw the completion of my first substantial free software project: a TLA⁺ grammar for tree-sitter, the error-tolerant incremental parser generator. The project stabilized & found users over the course of 2022, then over the holidays I used it to build the TLA⁺ Unicode Converter. The new year is a time to reflect on the past and look to the future, so here in early 2023 seems ideal to publish my experience. [Read More]

What's the difference between a computer and a rock?

What's the difference between a computer and a rock?
Author’s note: I wrote this in 2017 and it languished in the drafts since then because I couldn’t think of a good conclusion. Really this is typical of the subject matter and all this piece offers is something to chew on, if you have the interest in it or have never before considered the question. At the time I was helping tutor a TLA⁺ seminar and had the opportunity to ask Leslie Lamport (who has thought about computation quite a bit! [Read More]

The Missing Prelude to The Little Typer's Trickiest Chapter

Yes, it's the replace function in chapter 9

The Missing Prelude to The Little Typer's Trickiest Chapter
It’s hard to find a textbook series garnering more effusive praise than The Little Schemer, The Little Prover, The Little Typer & co. The Little Typer introduces dependent type theory and is the first of the series I’ve read. I quickly grew to appreciate & enjoy its dialogue-based presentation - I’m a real convert! I might release future didactic blog posts as a dialogue rather than straight recitation of material in block paragraphs. [Read More]

Regexes in the Z3 Theorem Prover

Analyzing Teleport RBAC

Regexes in the Z3 Theorem Prover
Republished from Teleport’s official blog (link). I received compensation from Teleport for writing this post. Z3 is a satisfiability modulo theories (SMT) solver developed by Microsoft Research. With a description like that you’d expect it to be restricted to esoteric corners of the computerized mathematics world, but it’s made impressive inroads addressing conventional software engineering needs: analyzing network ACLs and firewalls in Microsoft Azure, for example. Z3 is used to answer otherwise-unanswerable questions like “are these two firewalls equivalent? [Read More]

Two pictures of quantum computation

Quantum interference in the sum-over-paths formalism

Two pictures of quantum computation
Interpretations of quantum mechanics are boring. Boring! Maybe the universe has a strict partition between quantum and non-quantum. Maybe there are a bunch of parallel universes with limited crosstalk. Or maybe it’s whatever the Bohmian mechanics people are talking about. Shut up and calculate, I think. I don’t say this out of some disdain for idle philosophizing or to put on airs of a salt-of-the-earth laborer in the equation mines. It’s just there are so, so many interesting things you can learn about in quantum theory without ever going near the interpretation question. [Read More]

How do you reason about a probabilistic distributed system?

How do you reason about a probabilistic distributed system?
In which I am stunted upon by coin flips Wasn’t too long ago that I felt pretty good about my knowledge of distributed systems. All someone really needed in order to understand them, I thought, was a thorough understanding of the paxos protocol and a willingness to reshape your brain in the image of TLA⁺. Maybe add a dash of conflict-free replicated datatypes, just so you know what “eventual consistency” means. [Read More]

Meditation

Sadly my only weapon against the attention economy

Meditation
This isn’t going to be a post about how adopting a several-thousand-year-old practice can make you a better servant of capital. Instead, let’s talk about when I feel the lowest of the low. It comes after spending any number of hours on my computer, maybe even a full day, endlessly circling around different websites in search of stimulation, the quick jolt that comes with learning an interesting fact or watching a funny short video or seeing someone get dunked on for having a bad political opinion. [Read More]

Taking my home work setup seriously

Ergonomics & settling in for the long haul

Taking my home work setup seriously
The headlines don’t lie. Microsoft, Google, Amazon, Facebook, and a whole host of other tech companies have announced employees will be working from home until early-mid 2021. There are reasons to believe this will be pushed back; even if the staggeringly ambitious timelines for vaccine development are met, a vaccine might not be a silver bullet and the pandemic could require management for the next 2-3 years. As a software engineer in big tech’s orbit, this means it’s time to settle in for the long haul and take my home work setup seriously. [Read More]

Doing a math assignment with the Lean theorem prover

Doing a math assignment with the Lean theorem prover
Note: this post was written for Lean 3; the latest version, Lean 4, is a very different language. Turn back the clock to 2009: a confused physics major newly infatuated with math and computer science, I enrolled in MATH 273: Numbers and Proofs at the University of Calgary. This wasn’t my first encounter with mathematical proof; in first-year calculus I’d mastered rote regurgitation of delta-epsilon proofs. Despite writing out several dozen, their meaning never progressed beyond a sort of incantation I can summon to this day (for every \( \epsilon > 0 \) there exists a \( \delta > 0 \) such that…). [Read More]

Simulating physical reality with a quantum computer

Quantum chemistry for complete beginners

Simulating physical reality with a quantum computer
Quantum Computers: Not Just for Breaking RSA There’s no denying it, Shor’s algorithm was a blockbuster result. The thought of an exotic new computer breaking all widely-used public-key crypto plays well with the public imagination, and so you’d be forgiven for believing quantum computing is ultimately a sort of billions-dollar make-work project for software engineers: forcing our profession to relive a Y2K-like mass upgrade of old systems to new, quantum-safe encryption algorithms. [Read More]