Euclean Automates Geometry Problem Formalization in Lean

Linbin Tang, Jingyan You, Zilin Kang, Hanzhang Liu, Sophia Zhang, Zenan Li, Chenrui Cao, Liangcheng Song, Jiaao Wu, Xian Zhang, Fan Yang· July 23, 2026 View original

Summary

Euclean is a new framework that automates the formalization of geometry problems within the Lean theorem prover, unifying geometry with other mathematical domains. It introduces the largest geometry formalization datasets for Lean, significantly improving neural theorem proving performance.

Formal reasoning systems have achieved impressive performance, even reaching IMO-level capabilities, but the landscape remains fragmented. While algebra and number theory are well-supported in systems like Lean, geometry often relies on separate, domain-specific languages with limited formal guarantees. This division complicates unified model development and increases the trusted computing base. Existing efforts to integrate geometry into Lean have faced challenges, including incompatible axiom systems and limited scale. This paper introduces Euclean, a four-stage framework designed to automatically formalize geometry problems directly within Lean's native Mathlib environment. The process involves constraint explication, configuration anchoring, formalization mapping, and iterative repair. Euclean has been used to construct OMNI-Geometry (768 competition problems) and Numina-Geometry (177,597 problems), creating the largest geometry formalization datasets for Lean. Training the Goedel v2 theorem prover on these new datasets resulted in an improvement in proof success from 13.6% to 15.1%, validating the quality of the data for advancing unified neural theorem proving.

Why it matters

Unifying formal geometry within a robust theorem prover like Lean streamlines AI development for mathematical reasoning, enabling more powerful and versatile automated proof systems for complex problems.

How to implement this in your domain

  1. 1Explore using Euclean's framework for formalizing domain-specific knowledge in other complex areas.
  2. 2Leverage the OMNI-Geometry and Numina-Geometry datasets for training advanced AI theorem provers.
  3. 3Investigate integrating formal verification tools like Lean into critical software development pipelines.
  4. 4Collaborate with academic researchers on extending formalization techniques to new mathematical or logical domains.

Who benefits

AI DevelopmentSoftware EngineeringEducationResearch & DevelopmentAerospace

Key takeaways

  • Euclean unifies geometry formalization within the Lean theorem prover, addressing fragmentation.
  • It creates the largest geometry formalization datasets for Lean, improving AI theorem proving.
  • Automated formalization helps make implicit diagrammatic assumptions explicit.
  • Unified formal reasoning systems enhance the development of robust AI for mathematics.

Original post by Linbin Tang, Jingyan You, Zilin Kang, Hanzhang Liu, Sophia Zhang, Zenan Li, Chenrui Cao, Liangcheng Song, Jiaao Wu, Xian Zhang, Fan Yang

"arXiv:2607.19374v1 Announce Type: new Abstract: Recent formal reasoning systems have reached IMO-level performance, yet they leave a fragmented landscape: algebra and number theory are handled in Lean, while geometry still relies on domain-specific languages with limited formal g…"

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Originally posted by Linbin Tang, Jingyan You, Zilin Kang, Hanzhang Liu, Sophia Zhang, Zenan Li, Chenrui Cao, Liangcheng Song, Jiaao Wu, Xian Zhang, Fan Yang on X · view source

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