Top all-time · #4227
Andrew Helwer
Personal blog · ahelwer.ca/post · on HN as ahelwerprogrammingmathsystems
Andrew Helwer's personal blog at ahelwer.ca covers programming, math and systems. Since 2019, 18 different Hacker News readers have linked it 56 times, most often “Checking Firewall Equivalence with Z3”. It is still writing: the last post was on 2026-09-26, and you can follow it by feed.
Too few sampled comments (3) to say how often HN recommends it.?
Why HN links it
HN readers link Andrew Helwer's blog for posts on quantum chemistry on quantum computers, and for model checking and executable pseudocode (Python vs PlusCal). It also appears in an RSS feed roundup.
Summarised by Claude from a sample of 3 HN comments that link here. Each comment is marked recommending, critical or neutral (citing without judging); how this works.
Software engineer with over a decade of professional experience. Currently working as a Senior Software Engineer at Microsoft Azure Storage in Seattle, WA, USA. BSc in Computer Science from the University of Calgary. See my full résumé here. Technical interests include deterministic simulation testi
Most-linked posts?
- Checking Firewall Equivalence with Z33 people · 3 mentions · first linked 2021-05-05
- Two pictures of quantum computation (2020)2 people · 3 mentions · first linked 2020-12-10
- Simulating physical reality with a quantum computer2 people · 3 mentions · first linked 2019-12-26
- Writing a TLA⁺ Tree-sitter grammar2 people · 2 mentions · first linked 2023-01-12
- The changing role of finite-state model checking2 people · 2 mentions · first linked 2026-08-24
- Laptops all have built-in security tokens these days2 people · 2 mentions · first linked 2026-05-09
- Pseudocode Showdown: Python vs. PlusCal and TLA+2 people · 2 mentions · first linked 2023-03-30
- Can we have reachability properties in TLA⁺?2 people · 2 mentions · first linked 2026-09-26
- Book review: Is parallel programming hard, and, if so, what can you do about it?2 people · 2 mentions · first linked 2026-09-21
- Two C++ bugs I found2 people · 2 mentions · first linked 2023-02-05
What Hacker News says?
I wrote up an in-depth introduction to a different nonlocal game (CHSH) here: https://ahelwer.ca/post/2018-12-07-chsh/ It's a bit more complicated to follow but absolutely worth the work.
Comment linking /post/2018-12-07-chsh/
on “Landmark computer science proof cascades through physics and math”Submitted Book review: Is parallel programming hard, and, if so, what can you do about it? as a story · 149 points
HN discussionWell, I did it. I wrote an extended dialogue explaining the replace function as a blog post: https://ahelwer.ca/post/2022-10-13-little-typer-ch9/ I'd found your review a week or so ago which was nice since it reassured me I wasn't the only person having trouble with it.
Comment linking /post/2022-10-13-little-typer-ch9/
on “The Little Typer (2018)”Submitted The current state of TLA⁺ development as a story · 142 points
HN discussionGlad you enjoyed! I also wrote a couple of follow-up blog posts which examine quantum entanglement & quantum chemistry simulation, respectively: https://ahelwer.ca/post/2018-12-07-chsh/ https://ahelwer.ca/post/2019-12-21-quantum-chemistry/
Comment linking /post/2019-12-21-quantum-chemistry/
on “CERN Online introductory lectures on quantum computing from 6 November”Submitted Doing a math assignment with the Lean theorem prover as a story · 141 points
HN discussionI worked through this a few years ago and it is wonderful, but I found chapter 9 on the replace function totally impenetrable, so I wrote a blog post in the same dialogue style intended as a gentler prelude to it. A few people have emailed me saying they found it and it helped them. https://ahelwer.ca/post/2022-10-13-little-typer-ch9/
Comment linking /post/2022-10-13-little-typer-ch9/
on “The Little Typer (2018)”Submitted How do you reason about a probabilistic distributed system? as a story · 112 points
HN discussionI used Z3 at work to check equivalence of two sets of firewall rules https://ahelwer.ca/post/2018-02-13-z3-firewall/
Comment linking /post/2018-02-13-z3-firewall/
on “Programming in Z3 by learning to think like a compiler”Submitted Let go of StackOverflow; communities must take ownership as a story · 69 points
HN discussionLean is the basis for my favorite puzzle game of the past five years: https://wwwf.imperial.ac.uk/~buzzard/xena/natural_number_gam... It's like enemies & bosses are mathematical theorems you have to prove. Each time you slay one, you get it as a weapon you can use against further, more difficult bosses! The grand finale (Inequality World) is very memorable; such a feeling of accomplishment after I cracked it all. Th…
Comment linking /post/2020-04-05-lean-assignment/
on “Building the Mathematical Library of the Future”Submitted Taking my home work setup seriously: ergonomics and setting in for the long haul as a story · 22 points
HN discussionThis is something you can experimentally test. First you should know that "red ball or blue ball" is a simplification. Staying with the metaphor, if you open one envelope differently you might get a purple ball and so know the other envelope contains a green ball. What we're actually dealing with are vectors on the complex unit sphere instead of ball colors, and opening the envelope is choosing two perpendicular axe…
Comment linking /post/2018-12-07-chsh/
on “What did Einstein mean by “spooky action at a distance”?”Submitted Google Groups has been left to die as a story · 18 points
HN discussionI personally found this chapter very confusing, even with a good working knowledge of quantum computing - specifically the part about paths interfering destructively and canceling each other out. After a lot of thought and asking around I finally figured out what was going on with that diagram and wrote it up in a blog post: https://ahelwer.ca/post/2020-12-06-sum-over-paths/ Basically there are two ways of looking a…
Comment linking /post/2020-12-06-sum-over-paths/
on “PHYS771 Lecture 9: Quantum (2007)”Submitted A supposedly worthwhile contract I'll never do again as a story · 11 points
HN discussionI made a lecture aimed at such people (I was such a person!), which has proven popular: https://youtu.be/F_Riqjdh2oM With a follow-up blog post focusing on entanglement: https://ahelwer.ca/post/2018-12-07-chsh/
Comment linking /post/2018-12-07-chsh/
on “What makes quantum computing so hard to explain?”Submitted Can sanitizers find the two bugs I wrote in C++? as a story · 10 points
HN discussionI've certainly made the jump to a fully-thought-out home office[0], but masks are conspicuously absent from this article - facial recognition? Good luck when I continue wearing my nice face covering in public long after this specific virus is under control. Things like the virus-killing HVAC system are interesting. Makes you consider our current buildings from a future perspective, like in what ways they'll think we…
Comment linking /post/2020-08-09-home-ergonomics/
on “What coronavirus will do to our offices and homes”Submitted TLA⁺ is more than a DSL for breadth-first search as a story · 9 points
HN discussionI used to publish some math-heavy posts on medium (complete with equation images!) before moving it all over to gitlab pages with the hugo static site generator, and equations rendered with katex. If the author is reading this, the translation process didn't take very long (maybe a day) and I'm very happy with the results; compare: https://medium.com/@ahelwer/walking-the-faster-than-light-ti... https://ahelwer.ca/po…
Comment linking /post/2018-12-07-chsh/
on “Getting Started with Random Matrices: A Step-by-Step Guide”Submitted The changing role of finite-state model checking as a story · 4 points
HN discussionThis seems like a decent explanation of what I had in mind: https://oxsci.org/quantum-computing-for-quantum-chemistry/ and this one a slightly more math based explanation: https://ahelwer.ca/post/2019-12-21-quantum-chemistry/ I'm trying to recall another far less outlandish result (than wormholes) that was also verified via quantum computer, but no dice at the moment. Edit: I might've been thinking of the simulation…
Comment linking /post/2019-12-21-quantum-chemistry/
on “Google's quantum computer suggests that wormholes are real (2022)”Submitted Laptops all have built-in security tokens these days as a story · 4 points
HN discussionWell, it relays information in the same way that each of you using a random number generator pre-initialized with the same seed relays information. It doesn't involve faster-than-light communication, is the point. Entanglement differs from classical RNGs in that there is no shared seed; no local hidden variable, as it's called. The measurements are just... correlated. If you're interested in a deep dive on entanglem…
Comment linking /post/2018-12-07-chsh/
on “Quantum entanglement and the non-orientability of spacetime”Submitted Inlining SVGs for Dark Mode as a story · 4 points
HN discussionhttps://danluu.com/atom.xml https://googleprojectzero.blogspot.com/feeds/posts/default https://fasterthanli.me/index.xml https://ahelwer.ca/index.xml https://www.erlang.org/blog.xml https://drewdevault.com/blog/index.xml https://norvig.com/rss-feed.xml
Comment linking /index.xml
on “Ask HN: What are good RSS feeds you follow?”Submitted Meditation: Sadly my only weapon against the attention economy as a story · 4 points
HN discussionOh hey, I worked on this a while back. At the end of 2021 I also did work for Teleport extending this same approach and applying it to Role-Based Access Control rules. This was interesting because it exercised Z3's string analysis capabilities, even checking regular expressions for equivalence: https://ahelwer.ca/post/2022-01-19-z3-rbac/ People get intimidated by the terms SMT or theorem prover but I want to emphasi…
Comment linking /post/2022-01-19-z3-rbac/
on “Checking Firewall Equivalence with Z3”Submitted Can we have reachability properties in TLA⁺? as a story · 3 points
HN discussion
