Lean is an open source theorem prover and programming language being developed
at Microsoft Research. Lean aims to bridge the gap between interactive and
automated theorem proving, by situating automated tools and methods in a
framework that supports user interaction and the construction of fully specified
axiomatic proofs. The mathematical components library mathlib for Lean is being
developed at Carnegie Mellon University.

WWW: https://leanprover-community.github.io/