The first-ever Lean in Munich meetup happened this week! 🎥 Watch Sebastian Ullrich's full talk on Lean's foundations, software verification, and AI: youtube.com/watch?v=2Dr2149l_9Y #leanlang #leanprover #formalverification #mathematics

Mathematician @davidbessis.bsky.social once waited 7 years for a paper to get accepted. Not because it was wrong, but because it was too complex to verify. In a recent conversation Bessis explained to @curtjaimungal.skystack.xyz how Lean could change that: Watch: www.youtube.com/watch?v=GHGi...

CSLib just launched — an open-source effort to formalize computer science in Lean, inspired by Mathlib. CS researchers, practitioners & enthusiasts are invited to get involved! Learn more at: 🌐 cslib.io 🤝 Contribute: github.com/leanprover/c... #LeanLang #LeanProver #CSLib #FormalVerification

Lean 4.28.0 is out! New symbolic simulation framework for 𝚐𝚛𝚒𝚗𝚍, user-defined 𝚐𝚛𝚒𝚗𝚍 attributes for custom tactics, a new 𝚜𝚘𝚕𝚟𝚎𝚛𝙼𝚘𝚍𝚎 in 𝚋𝚟_𝚍𝚎𝚌𝚒𝚍𝚎 for proof vs. counterexample search, and lean4checker available out of the box. lean-lang.org/doc/referenc... #LeanLang #LeanProver #ProofAssistant

The next bi-monthly #Mathlib community meeting is tomorrow Friday, 13th at 3pm UTC. Join to hear about ongoing #LeanLang formalization projects and connect with other contributors! ➡️ See all upcoming community events on our website: lean-lang.org/community/#e...

Terence Tao on how math is changing, #formalverification as the enabler of scaled human-AI collaboration: "The reason why scaling and AI and broad participation actually is a net win is because we have formal verification." 📺 www.youtube.com/watch?v=SuTx... #leanlang #leanprover

The next Lean FRO office hours are Feb. 11 at 4pm UTC. Bring your questions, share your projects, or just come to learn from others in the community! See our full calendar here: lean-lang.org/community/#e... #LeanLang #LeanProver

From The Geometry of Machine Learning at Harvard CMSA in Sept: Jared Duker Lichtman's talk explores Math, Inc. Gauss's contributions to number theory and how these results are being formalized in #LeanLang. Watch here: www.youtube.com/watch?v=Ko-P...

Looking for a lemma in #LeanLang / #Mathlib but don't know its name? Use Loogle! to search: By pattern: _ * (_ ^ _) finds expressions matching the pattern By conclusion: |- tsum _ = _ * tsum _ finds specific conclusion shapes Combine searches with commas for precision! loogle.lean-lang.org

𝐋𝐞𝐚𝐧 𝟒.𝟐𝟒.𝟎 𝐢𝐬 𝐥𝐢𝐯𝐞! This release improves the module system, strengthens the 𝚐𝚛𝚒𝚗𝚍 tactic, and advances the standard library. Key improvements: 3.5x faster auto-completion, streamlined "try this" suggestions, new 𝚐𝚛𝚒𝚗𝚍 AC solver, enhanced 𝚖𝚟𝚌𝚐𝚎𝚗 syntax. Read more: lean-lang.org/doc/referenc...

Tactic tip: Lean's 𝚜𝚒𝚖𝚙? is an optimization tool that shows the minimal 𝚜𝚒𝚖𝚙 𝚘𝚗𝚕𝚢 call needed to close a goal. Use the 𝚜𝚒𝚖𝚙? "Try this" suggestion to insert the precise 𝚜𝚒𝚖𝚙 𝚘𝚗𝚕𝚢 call into your proof. Learn more: lean-lang.org/theorem_prov... #LeanLang #LeanProver #ProofAssistant

"Theorem Proving in Lean 4" is the essential guide for anyone using Lean for mathematical proofs. Kept up-to-date with each new Lean release, it covers everything from basic tactics to advanced proof strategies. Read the book here: lean-lang.org/theorem_prov... #LeanLang #LeanProver #Mathematics

Reservoir is #LeanLang's package registry, inspired by crates.io (thanks @rustfoundation.org!) Browse community-created packages and discover new tools: reservoir.lean-lang.org Sharing is easy! GitHub repos meeting the inclusion criteria are auto-indexed: reservoir.lean-lang.org/inclusion-cr...

Speed up your #LeanLang workflow in #VSCode with shortcuts: ℹ️Ctrl/Cmd+Shift+Enter: Open the InfoView 🔡Ctrl/Cmd+Shift+O: List current file declarations, namespaces and sections 🔄Ctrl/Cmd+Shift+X: Restart the current file See more in the Lean VS Code extension manual: github.com/leanprover/v...

#LeanLang office hours are tomorrow (Wednesday the 15th) at 23:00 UTC. Bring your questions, share your projects, or just come to learn from others in the community. ➡ Find calendar and meeting links on our website: lean-lang.org/community/#e...

New use case on our website: AWS's Cedar authorization policy language verified with Lean, using "verification-guided development", and integrated into Cedar's development workflow. ➡️Read more: lean-lang.org/use-cases/ce... #LeanLang #LeanProver #CedarPolicy #FormalVerification #AWS

We’re pleased to announce #ItaLean2025: Bridging Formal Mathematics and AI, an international conference dedicated to @lean-lang.org, Formal Mathematics, and AI4Math. 📍 University of Bologna 🗓 9–12 December 2025 Proudly supported by #Harmonic. #LeanLang #FormalMath #AI4Math

💡Did you know you can run #LeanLang in your browser without installing anything? The Lean Playground provides a full environment for experimentation, learning, and for sharing code snippets with others. Try it out! live.lean-lang.org

The next bi-monthly #Mathlib community meeting is tomorrow (Friday Oct 10) at 2pm UTC. Join to hear about ongoing #LeanLang formalization projects and connect with contributors. See all community events on our website: lean-lang.org/community/?u...

Did you know the Info View in #LeanLang's #VSCode extension updates in real-time as you write proofs? Click on any part of your code to see the current proof state, goals, and hypotheses at that exact point. Learn more about the Lean VS Code extension: github.com/leanprover/v...

We really loved this series of tutorials on #metaprogramming in #LeanLang by Heather Macbeth. It's a great intro to a complex topic for novice users of #LeanProver! Pt 1: youtube.com/watch?v=cKvg... Pt 2: youtube.com/watch?v=5er4... Pt 3: youtube.com/watch?v=TJ8T...

Two great talks at #HLF25 last week: Sanjeev Arora on superhuman AI mathematicians using #LeanLang, and David Silver on AI learning through experience with #LeanProver verification. www.youtube.com/watch?v=q9MJ... #AI #FormalMath #ReinforcementLearning

ICYMI: A great summary on the #LeanLang Community Blog of the @simonsfoundation.org 2025 MPS (Math and Phys Sciences) Workshop on #LeanProver. The post includes links to lecture slides, videos, and a list of proposed projects and participants! leanprover-community.github.io/blog/posts/s...

Fun to see snippets of #LeanLang interspersed into this fantastic @3blue1brown.com guest video by @bensyversen.bsky.social about Euclid's Elements!

🎉 Lean 4.23.0 is here! Includes many usability improvements, including: 🎯 Enhanced 'Go to Definition' supporting type class instances 🔧 Interactive error hints for faster debugging Release notes: lean-lang.org/doc/referenc... #LeanLang #LeanProver #OpenSource #Mathematics #FormalVerification

Recently came across @filiplajszczak.bsky.social's series formalizing a 1967 math textbook in #LeanLang. Designed for those "with no prior experience with formalization" - nice bridge for newcomers to #LeanProver! Read the intro post here: filip.lajszczak.dev/lean-4-with-...

⚛️📝 New on Overreacted: Lean for JavaScript Developers

If you're you curious about #LeanLang and want to understand the connection between #programming and #proofs, check out this great new video by Ank Yog. The analogy between Chess and true propositions is particularly compelling! www.youtube.com/watch?v=QXQN...

🎉 Lean 4.22.0 is here! It represents the culmination of our Year 2 roadmap! Including: 🧠 New grind tactic (SMT-style automated reasoning) 🏗️ New compiler (major performance foundation) Read the release notes: lean-lang.org/doc/reference/latest/releases/v4.22.0/ #LeanLang #LeanProver

A refreshingly nuanced take on AI v. the International Math Olympiad by none other than Emily Riehl (@emilyriehl.bsky.social) for @sciam.bsky.social

Just saw this post on LinkedIn about a new #DiscreteMath game on the #LeanLang Game Server. The author, Shrey Vivek, won a "Best Poster" award at the SPMS Odyssey Research Symposium. 🎉 The Discrete Math game: adam.math.hhu.de#/g/shreyvive... The LinkedIn post: www.linkedin.com/posts/shrey-...

Thorsten Altenkirch explains Gödel's Incompleteness Theorem on @computerphile.bsky.social, and shows some definitions in #LeanLang! 🎯 Watch here: www.youtube.com/watch?v=IuX8...

We're excited to share the Lean FRO Year 3 Roadmap today! It builds on work completed in the first two years of Lean FRO operations and will guide all #LeanLang development through July 2026. ➡️ Read the roadmap at lean-lang.org/fro/ #LeanProver #FormalMathematics #FormalVerification

The first volume of the new Open Access journal "Annals of Formalized Mathematics" was released today! ➡️ afm.episciences.org/volume/view/... #FormalMath #Mathematics #OpenAccess

IMO 1996 P3: Lean 4 formalization. ~ David Renshaw. youtu.be/5NbYtDfXfR4 #ITP #LeanProver #Math

Markus Himmel has written a blog post about how to write a simple imperative program in Lean and then how to verify that the program is bug-free. markushimmel.de/blog/my-firs...

In the continuing saga of surprising things users do: This post over on LinkedIn features a custom made #LeanLang environment intended to replace a Jupyter Notebook, because, you know - why not? 👀 www.linkedin.com/posts/philip... (With apologies to @jupyter.org ❤️)

This is an... unexpected use of the #LeanLang InfoView: unnamed.website/posts/bad-ap... But we love the creativity! #LeanProver #DevTools #Metaprogramming

📣 We're excited to share the new lean-lang.org! Relaunching our website was a key deliverable in our Year 2 roadmap to provide "improved navigation and access to valuable content, resources, and tools." We hope you like it! #LeanLang #LeanProver

Computers can check whether mathematical proofs are correct, but only if they have been translated into a machine-readable form first. Now, AI has got surprisingly good at this translation - which could transform the way maths is done.

Really enjoyed this talk by @harrisongoldste.in that demonstrates inventive uses of the #LeanLang InfoView enhanced by metaprogramming techniques to display real-time testing data. #LeanProver #Metaprogramming #VSCode #PropertyTesting

📣 #LeanLang v4.21 is released! This release brings 295 changes, including feature additions, bug fixes, refactors, documentation improvements and performance improvements, in support of our Y2 roadmap: lean-fro.org/about/roadma... ➡️ See the full changelog here: lean-lang.org/doc/reference/

Core Memory #22 with @ashleevance.bsky.social features a conversation with @adammarblestone.bsky.social and @anastasiag.bsky.social on science funding and FROs with a segment on #LeanLang and its importance to formal verification and AI research. 🎥 www.youtube.com/watch?v=Gbu6...

In this 10-minute UCLA Connect talk, Terence Tao provides an accessible and compelling argument for "citizen math" and broad collaboration in research #mathematics via #formalverification using proof assistants like #LeanLang. 🎥 www.youtube.com/watch?v=K376...

Incredibly grateful to @sigplan.bsky.social and @sigplan-pldi.bsky.social for awarding #LeanLang the Programming Languages Software Award 2025 at #PLDI2025! #LeanProver #FormalMethods #ProgrammingLanguages #Mathematics #SoftwareVerification

Lean won the SIGPLAN Programming Languages Software Award 2025 #LeanLang #LeanProver In a few days there will be a much better text at @lean-lang.org's site, but here is all I could gather today: dev.to/adolfont/lea...

Cryspen is excited to announce it has been awarded a grant from the Ethereum Foundation to extend our hax verification toolchain with support for the Lean prover. Watch this space for more on this soon! #FormalVerification #Lean #Rust

📣 This week, #LeanLang Chief Architect Leonardo de Moura will deliver a keynote in Seoul at #PLDI2025 titled "Lean: Machine-Checked Mathematics and Verified Programming, Past and Future." #pldi #formalmethods #programminglanguages #leanprover

🎉 #LeanLang 0.1 was released 11 years ago today! Lean had been in development since July 15, 2013, but Lean 0.1 was a major milestone. The screencap is a @waybackmachine.bsky.social 06/26/2014 snapshot from the @lean-lang.org GitHub, "Updated 10 days ago"! #LeanProver #ProgrammingHistory

If you're interested in keeping up on #LeanLang / #LeanProver news check out the LeanLang feed by @adolfont.github.io! bsky.app/profile/did:...