Short answers, pulled from the story.
Brazilian computer scientist Leonardo de Moura developed the Lean proof assistant while working at Microsoft Research. The system officially launched in 2013 as a new tool for formal verification.
Engineers rebuilt the entire prover from scratch using Lean as the primary language instead of relying on C++ code. This decision allowed users to override key parts of the system without accessing low-level C++ sources and enabled generation of executable C code.
By May 2025 the mathlib project effort had formalized more than 210,000 theorems and 100,000 definitions within the framework. Community contributors maintain this extensive library alongside complementary packages like batteries for additional data structures.
Google DeepMind released AlphaProof in 2024 achieving silver medalist performance at International Mathematical Olympiad competitions. This marked the first time any AI system reached medal-worthy standards on math olympiad problems before DeepSeek introduced DeepSeek-Prover-V2 in April 2025.