There's Mathlib: https://leanprover-community.github.io/mathlib_docs/index.html https://leanprover-community.github.io/mathlib_docs/index.ht... I was stunned w

There's Mathlib: https://leanprover-community.github.io/mathlib_docs/index.html https://leanprover-community.github.io/mathlib_docs/index.ht... I was stunned when I discovered it, because it does exactly what its name suggests: it's a huge library of math proofs available as a library in Lean.