Lean
Software
Proving theorems to formally verify that code is correct
"We're using Lean. If you don't know what that is, you know, climb out from under a rock. Lean is a great theorem proving system. It basically is a system that lets you check... the system itself checks every step. It doesn't let you make a mistake."
More source quotes
Formalizing and machine-verifying his mathematical and physics work so critics can check it
"I am so excited about the fact that I'm finally going to have something I can talk to, the formalization project. I've been alerted to this by a guy named Jared Lichtman, who's a professor at Stanford... I can translate everything I've done into this progra..."
Formal mathematical problem solving and proof verification
"we take 3,000 formal math problems. So this is just in lean for you can write out the problem statement in this coding language in math"