Lean Focused Research Organization

Software Verification in Lean on November 7 has reached in-person capacity! If you're interested in attending live, please join the waitlist: A livestream link will be shared with all waitlisted registrants a few days before the event.

Lean 4.35.0 is now available, with 214 changes. It adds vcgen, the successor of mvcgen, and lake check, which checks a project with Lean's kernel and, with --paranoid, several external checkers. lean-lang.org/doc/referenc...

Lean 4.34.0 is out: 159 changes. Three kernel soundness vulnerabilities fixed, all requiring deliberately constructed inputs rather than ordinary code. 𝚋𝚟_𝚍𝚎𝚌𝚒𝚍𝚎 is up to 6x faster. lean-lang.org/doc/referenc...

The Lean FRO Year 4 Part 1 roadmap, covering September 2026 through February 2027, is now published. It sets out our priorities for Lean and ecosystem support for the first half of our fourth year of operations. 🔗 Read the full roadmap here: lean-lang.org/fro/roadmap/... #LeanLang #LeanProver

Lean 4.33.0 is live! 208 changes: a smoother editor, automatic try? suggestions, and Float finally has a logical model instead of staying opaque. Full notes: lean-lang.org/doc/referenc... #LeanLang #LeanProver

Lean 4.32.0 is live. 102 changes, including the new do elaborator now on by default, a new module linter framework, and roughly a 10% speedup importing Mathlib. Full release notes: lean-lang.org/doc/referenc... #LeanLang #LeanProver #FormalVerification

We're grateful that @simonsfoundation.org has included Lean in three articles of their 2025 annual report. President David Spergel calls it "a proof assistant that brings rigorous machine-verified structure for testing theorems." 📄 www.simonsfoundation.org/series/2025-...

Lean 4.31.0 is live! 305 changes: verifiable do-block loops with no source changes required, mvcgen' (100x+ faster than mvcgen on some benchmarks), and lake lint with Batteries/Mathlib linters built in. lean-lang.org/doc/referenc... #LeanLang #LeanProver #OpenSource

Two online panels for the launch of The Proof in the Code, @kevinhartnett.bsky.social's new book on Lean and Mathlib. The Mathematicians, June 11. The Builders, June 12. Both 5pm UTC. Learn more and register: The Mathematicians: forms.gle/w16jkmsMqB2g... The Builders: forms.gle/PsxPkq3x2pES...

Lean 4.30.0 is live! 306 changes: new 𝚜𝚢𝚖 => interactive tactic (𝚐𝚛𝚒𝚗𝚍-based, user-controlled), 𝚌𝚋𝚟 out of experimental, LCNF backend complete (~15% smaller binaries), and a full Lake cache overhaul. Release notes: lean-lang.org/doc/referenc...

SVIL in Lean 2026 recordings are now available. Max Tegmark on Signal Shot: "Everybody should be able to be secure." Watch: www.youtube.com/watch?v=eTCW...

The Beneficial AI Foundation asks: "Can we prove that Signal's cryptography is secure — not just on paper, but in actual code?" Signal Shot, launched today, aims to find out. Open to contributions. 🔗 beneficialaifoundation.org/blog/signal-shot #leanlang #leanprover #softwareverification

🚀 Lean 4.29.0 is out! Faster startup, simpler 𝚗𝚘𝚗𝚌𝚘𝚖𝚙𝚞𝚝𝚊𝚋𝚕𝚎 semantics, higher-order Miller pattern support in 𝚐𝚛𝚒𝚗𝚍, and a significant overhaul to reducibility and instance handling. 453 changes! 🔗 lean-lang.org/doc/reference/latest/releases/v4.29.0/ #LeanLang #LeanProver

The Lean Y3 roadmap is building infrastructure to keep performance "visible and actionable." Radar automatically benchmarks every commit and compares it to previous ones to catch regressions and improvements. See more: radar.lean-lang.org/about #LeanLang #LeanProver

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...

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