Lean 3 material for Kevin Buzzard's 2021 TCC courrse on formalising mathematics. Lean 4 version available here: https://github.com/ImperialCollegeLondon/formalising-mathematics-2024
Why do you think that https://github.com/ImperialCollegeLondon/formalising-mathematics-2022 is a good alternative to formalising-mathematics