Ilya Sergey

New post on "Proofs and Intuitions": Verus meets Lean. An experiment in bringing interactive proofs and mathematical libraries to auto-active Rust verification. proofsandintuitions.net/2026/10/18/v...

A two-weekend fun project from 2 months ago: Vermilion, an experimental Lean 4 backend for Verus verifier for Rust. Verification conditions are readable Lean theorems, provable with an SMT solver, Lean's grind, Mathlib lemmas, by hand, or by your favorite AI system. github.com/ilyasergey/v...

New to the LangLib: JavaGen, a language of nothing but Java interfaces and one subtype query, which is just enough to compute anything by a clever co/contra-variance interplay. Bonus: a Lean proof that Java generics are Turing-complete (Grigore, POPL'17). github.com/ilyasergey/l...

A new post: "When the Hard Part Stops Being Hard". The gist: the effort that used to be required for a publishable PL result can now be fully automated with AI, and the field's research culture is already changing because of it. proofsandintuitions.net

New blog post on Proofs and Intuitions: "Liveness Proofs in Veil, Part I: The First Step" (by Qiyuan Zhao). proofsandintuitions.net/2026/06/24/l... Safety says nothing bad happens; liveness says something good eventually does. We present a proof mode for verifying liveness deductively in Lean.

New blog post: On the Unreasonable Effectiveness of Property-Based Testing for Validating Formal Specifications. proofsandintuitions.net/2026/05/18/p... The gist: randomised testing can validate formal specs. It's very cheap and powerful: we found bugs in specs of VERINA and CLEVER benchmarks.

1/3 New Lean use case: Veil, a multi-modal verification framework for distributed protocols from George Pîrlea, Vladimir Gladshtein, Elad Kinsbruner, Qiyuan Zhao, and Ilya Sergey at NUS.

Are paper rejections really that bad? My papers get read by ~3 people on average. Each rejection means a resubmission, which means 3 more readers. After 4 rejections, that's double-digit readership.

New on "Proofs and Intuitions": Verifying Move Borrow Checker in Lean: an Experiment in AI-Assisted PL Metatheory. proofsandintuitions.net/2026/03/18/m... The gist: I formalised Move's type system in Lean: 39KLOC, under a month, with Claude. Person-years in PL research just became person-weeks.

New post on "Proofs and Intuitions": Verifying Distributed Protocols in Veil. We take a tour of Veil, a Lean-based verification framework that combines TLA+-style model checking with formal proofs and enables AI-powered invariant inference. proofsandintuitions.net/2026/02/09/d...

Implementing proof systems in Lean in 2026 be like

My research lab is launching a new blog, where we will share thoughts and tutorials on formal methods, mechanised proofs, PL, and more. proofsandintuitions.net First post: verifying imperative programs in Lean 4 with Velvet, using symbolic automation and AI-assisted proving.

Claude Code and Aristotle are my two new favourite backend solvers for auto-active program verification in Lean. AI is the new SMT.

Revisiting CS101.

Had a fantastic week teaching Programming with Proofs in Lean at Neapolis University Pafos. It was great to introduce NUP students to program verification with Veil and Velvet, having many insightful discussions along the way. Excited to see what projects they'll develop next!

We are hiring! Suzanne Embury and I are looking for a talented Ph.D. student 👩‍🎓👨‍🎓 to join an exciting, high-impact project on automated testing and bug fixing of Formal Methods tools. www.findaphd.com/phds/project...

Spent the last couple of days porting my program verification class from Dafny to Lean via Loom/Velvet, and it just works! Whenever the SMT solver can’t fully prove a program correct, Lean’s aesop and grind take care of the remaining goals.

Grokipedia is alright.

A reminder that we will have another @icfp-conference.bsky.social/SPLASH nature walk planned for tomorrow. Consider joining if you are (still) in Singapore! 2025.splashcon.org/attending/ou...

The tunes of Rocq’n’Roll. #icfpsplash25

FARM Performance is about to start! #icfpsplash25

Lots of folks in the OxCaml tutorial! #icfpsplash25

@icfp-conference.bsky.social Had a nice day co-hosting the first hike of #icfpsplash25 Outdoor Activities track with Yibo🙌 Walking in the forest 🌳 Seeking special animals (monkeys🐒, lizards🦎, colugos🦇, and even a snake🐍!) Enjoying the networking🥳

It seems the first hike as part of @icfp-conference.bsky.social/SPLASH went well! A shoutout to @ningkeli.bsky.social and Yibo DONG (as well as my wife, Ting), who guided the participants on this walk. I could unfortunately not participate, as I had to travel abroad due to an urgent issue.

1st coffee break of the week many many more to come #icfpsplash25

ICFP/SPLASH is starting now!! See you all at NUS today — #icfpsplash25

The UBC Software Practices Lab is heading to #icfpsplash25! 4 ICFP/OOPSLA talks, 1 SPLASH-E, 5 talks at associated workshops... check it out: www.cs.ubc.ca/news/2025/10...

A beautiful day to stop in at the Singapore Botanic Gardens and the National Orchid Garden before ICFP/SPLASH! #icfpsplash25

ICFP/SPLASH'25 is starting tomorrow! Attending Sunday workshops and FARM Performance at #icfpsplash25? Make sure check out our illustrated guide on getting to NUS Conservatory and dining options on campus: conf.researchr.org/venue/icfp-s...

I am thrilled to announce Velvet: a new foundational multi-modal verifier for imperative programs in Lean. Velvet unifies execution, testing, automated and interactive proofs; and is itself proven sound. 💻 github.com/verse-lab/loom 📄 verse-lab.github.io/papers/loom-...

One week until ICFP/SPLASH’25! conf.researchr.org/home/icfp-sp...

@mathieu.social will be presenting a functional pearl "Invertible Syntax without the Tuples", joint work with Arnaud Spiwack, at Olivier Danvy's Festschrift on the Tuesday 14th. conf.researchr.org/details/icfp...

And if you’re interested in OxCaml, we have a tutorial on Sunday at ICFP walking through it conf.researchr.org/track/icfp-s... (materials will be online for anyone afterwards. Just the minor detail of finishing writing them first)

An opening theme from the Outlaw Star series has just randomly started playing in my head, and now I am fighting the urge to rewatch it.

I’m looking for an intern to work on Rust/RustRover content creation. If you are a university student in any EU country, the UK, Serbia, or Armenia, and you are passionate about Rust and sharing your knowledge, I’d love to hear from you. Please repost to help spread the word. Links below.

T minus 3 weeks!! I wonder how many ICFP 2025 papers I can read on the plane ride over?

Now that the competition is over, Adso has penned his reflections. icfpcontest2025.github.io/afterword.pdf We also have many team write-ups here: icfpcontest2025.github.io/writeups.html Please let us know if you have some to add to the list!

Just visited YST Conservatory of NUS, the venue for the upcoming FARM concert at ICFP/SPLASH'25. Excited about the upcoming performance combining art, music, and creative programming! 2025.splashcon.org/track/splash...

OlivierFest’25 is taking place on October 14-15 at ICFP/SPLASH'25 in Singapore! A two-day celebration of Olivier Danvy's impact on PL research, with a program packed with talks on algebraic effects, semantics, interpreters, and, of course, continuations. conf.researchr.org/home/icfp-sp...

It's official: RTFM, the faculty mentoring workshop, is happening again, this time at POPL 2026 in Rennes. The one we had at PLDI 2024 in Copenhagen was well received, so I'm looking forward to the next edition. Stay tuned!