We already have a basic form of machine checked-proofs in everyday code: type systems. Type systems encode and prove simple theorems like "f(x: int) -> int returns an int, if x is an int". Typescript and Mypy show us that these proof checkers don't need to be built into a language. Even better, they show that proofs can be over subsystems of a program, since Typescript and Mypy both allow for partial/incremental typing. We just need to extend these systems to support more complex theorems.