The reporter says Mario Carneiro’s open-source vision for Mathlib clashed with Leo’s vision for Lean, and that this friction contributed to Leo’s distance from mathematicians between 2018 and 2022.

“Mario's vision is what he wants math lib to look like. He's very much a big open source believer. Leo's vision is for like Lean. The two of them clash quite a lot and in certain ways kind of, uh, that friction pushes Leo away from the mathematicians in this way in this 2018 to 2022 period.”