# Lean

> software for interactive and automated theorem proving

**Wikidata**: [Q6509476](https://www.wikidata.org/wiki/Q6509476)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Lean_(proof_assistant))  
**Source**: https://4ort.xyz/entity/lean

Here’s the structured knowledge entry for **Lean**:

---

## Summary  
Lean is an open-source software tool designed for interactive and automated theorem proving. It functions as both a proof assistant and a programming language, developed primarily by computer scientist Leonardo de Moura at Microsoft Research. Lean is widely used for formal verification of mathematical proofs and software correctness.

## Key Facts  
- **Developed by**: Leonardo de Moura (American computer scientist) at Microsoft Research.  
- **Inception**: 2013.  
- **License**: Apache Software License 2.0.  
- **Latest stable version**: 4.2.0 (released October 31, 2023).  
- **Platform**: Cross-platform (works on multiple operating systems).  
- **Programming paradigm**: Functional programming with dependent types.  
- **Influenced by**: Rocq prover and Isabelle.  
- **Website**: [https://lean-lang.org/](https://lean-lang.org/).  
- **Source code**: Hosted on GitHub ([Lean 4](https://github.com/leanprover/lean4)).  

## FAQs  
### Q: What is Lean used for?  
A: Lean is primarily used for interactive and automated theorem proving, enabling formal verification of mathematical proofs and software correctness.  

### Q: Who created Lean?  
A: Lean was developed by Leonardo de Moura, a computer scientist at Microsoft Research, with its first release in 2013.  

### Q: Is Lean free to use?  
A: Yes, Lean is open-source and distributed under the Apache Software License 2.0.  

## Why It Matters  
Lean represents a significant advancement in formal verification, bridging the gap between mathematical rigor and computational proof-checking. Its ability to handle dependent types and automate complex proofs makes it invaluable for researchers and developers working on high-assurance systems. Lean has influenced modern proof assistants and is actively used in academia and industry for verifying algorithms, cryptographic protocols, and mathematical theorems. Its cross-platform nature and open-source model further democratize access to formal methods.

## Notable For  
- **Dependent types**: Supports advanced type systems for rigorous proof construction.  
- **Cross-platform**: Works seamlessly across different operating systems.  
- **Award-winning**: Received the Programming Languages Software Award in 2025.  
- **Active development**: Regularly updated, with Lean 4 being a major rewrite.  
- **Community-driven**: Hosted on GitHub with contributions from researchers worldwide.  

## Body  
### Development  
- **Initial release**: 2013.  
- **Key developer**: Leonardo de Moura (also known for Z3 theorem prover).  
- **Primary institution**: Microsoft Research.  

### Technical Features  
- **Programming language**: Functional, with dependent types.  
- **File formats**: Lean 3 and Lean 4 file formats.  
- **Influences**: Inspired by Rocq prover and Isabelle.  

### Versions  
- **Lean 3**: Stable versions from 3.0.0 (2017) to 3.4.2 (2019).  
- **Lean 4**: Major rewrite, latest stable version 4.2.0 (2023).  

### Community & Resources  
- **Official website**: [lean-lang.org](https://lean-lang.org/).  
- **Interactive demo**: [live.lean-lang.org](https://live.lean-lang.org/).  
- **Support**: Stack Overflow and Proof Assistants Stack Exchange tags available.  

## Schema Markup  
```json
{
  "@context": "https://schema.org",
  "@type": "SoftwareApplication",
  "name": "Lean",
  "description": "Open-source software for interactive and automated theorem proving.",
  "url": "https://lean-lang.org/",
  "sameAs": [
    "https://www.wikidata.org/wiki/Q20720808",
    "https://en.wikipedia.org/wiki/Lean_(proof_assistant)"
  ],
  "applicationCategory": "Proof Assistant",
  "operatingSystem": "Cross-platform",
  "license": "Apache Software License 2.0",
  "programmingLanguage": "Lean",
  "author": {
    "@type": "Person",
    "name": "Leonardo de Moura"
  },
  "dateCreated": "2013"
}

## References

1. [Source](https://lean-lang.org/documentation/)
2. [Programming Languages Software Award](https://www.sigplan.org/Awards/Software/#2025_Lean_Theorem_Prover)
3. [Source](https://lean-lang.org/about/)
4. [Release 3.0.0. 2017](https://github.com/leanprover/lean/releases/tag/v3.0.0)
5. [Release 3.1.0. 2017](https://github.com/leanprover/lean/releases/tag/v3.1.0)
6. [Release 3.2.0. 2017](https://github.com/leanprover/lean/releases/tag/v3.2.0)
7. [Release 3.3.0. 2017](https://github.com/leanprover/lean/releases/tag/v3.3.0)
8. [Release 3.4.0. 2018](https://github.com/leanprover/lean/releases/tag/v3.4.0)
9. [Release 3.4.1. 2018](https://github.com/leanprover/lean/releases/tag/v3.4.1)
10. [Release 3.4.2. 2019](https://github.com/leanprover/lean/releases/tag/v3.4.2)
11. [Release 4.0.0. 2023](https://github.com/leanprover/lean4/releases/tag/v4.0.0)
12. [Release 4.1.0. 2023](https://github.com/leanprover/lean4/releases/tag/v4.1.0)
13. [Release 4.2.0. 2023](https://github.com/leanprover/lean4/releases/tag/v4.2.0)
14. [Release 4.3.0. 2023](https://github.com/leanprover/lean4/releases/tag/v4.3.0)
15. [Release 4.4.0. 2023](https://github.com/leanprover/lean4/releases/tag/v4.4.0)
16. [Release 4.5.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.5.0)
17. [Release 4.6.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.6.0)
18. [Release 4.6.1. 2024](https://github.com/leanprover/lean4/releases/tag/v4.6.1)
19. [Release 4.7.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.7.0)
20. [Release 4.8.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.8.0)
21. [Release 4.9.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.9.0)
22. [Release 4.9.1. 2024](https://github.com/leanprover/lean4/releases/tag/v4.9.1)
23. [Release v4.10.0 · leanprover/lean4](https://github.com/leanprover/lean4/releases/tag/v4.10.0)
24. [Source](https://github.com/leanprover/lean4/releases/tag/v4.11.0)
25. [Release 4.12.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.12.0)
26. [Release 4.13.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.13.0)
27. [Release 4.14.0. 2024](https://github.com/leanprover/lean4/releases/tag/v4.14.0)
28. [Release v4.15.0 · leanprover/lean4](https://github.com/leanprover/lean4/releases/tag/v4.15.0)
29. [Release 4.16.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.16.0)
30. [Release 4.17.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.17.0)
31. [Release 4.18.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.18.0)
32. [Release 4.19.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.19.0)
33. [Release 4.20.1](https://github.com/leanprover/lean4/releases/tag/v4.20.1)
34. [Release 4.20.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.20.0)
35. [Release 4.21.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.21.0)
36. [Release 4.22.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.22.0)
37. [Release 4.23.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.23.0)
38. [Release 4.24.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.24.0)
39. [Release 4.25.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.25.0)
40. [Release 4.25.1. 2025](https://github.com/leanprover/lean4/releases/tag/v4.25.1)
41. [Release 4.24.1. 2025](https://github.com/leanprover/lean4/releases/tag/v4.24.1)
42. [Release 4.25.2. 2025](https://github.com/leanprover/lean4/releases/tag/v4.25.2)
43. [Release 4.26.0. 2025](https://github.com/leanprover/lean4/releases/tag/v4.26.0)
44. [Release 4.27.0. 2026](https://github.com/leanprover/lean4/releases/tag/v4.27.0)
45. [Release 4.28.0. 2026](https://github.com/leanprover/lean4/releases/tag/v4.28.0)
46. [Release 4.29.0. 2026](https://github.com/leanprover/lean4/releases/tag/v4.29.0)
47. [Source](https://github.com/leanprover/lean4)