Lean (proof assistant)

Source code:

They are huge fans of Unicode characters! Check this out from a formal proof of the prime number theorem: github.com/AlexKontorovich/PrimeNumberTheoremAnd/blob/fbdbb5310d036d33b9797b35f3b04b08f2447a6e/PrimeNumberTheoremAnd/ZetaBounds.lean

Their dependency graph thingy is just beautiful however: alexkontorovich.github.io/PrimeNumberTheoremAnd/web/dep_graph_document.html