[kmill]

That's Lean 3, from eight years ago, and it's from before 'sorry' really existed in the way we know it now.

---

To answer the GP's question: Not only is there a verification mode, but Lean generates object files with the fully elaborated definitions and theorems. These can be rechecked by the kernel, or by external verifiers. There's no need to trust the Lean system itself, except to make sure that the theorem statements actually correspond to what we think they're supposed to be.

[treyd]

What exactly do these object files look like?

[kmill]

The "olean" files are a binary format that contain everything that was added to the Lean environment. Among other things, it includes all of the declarations and their Lean.Expr [1] expressions. People have written tools to dump the data for inspection [2], or to independently check that the expressions are type correct and the environment is well-formed (that is, check the correctness).

[1] https://github.com/leanprover/lean4/blob/3a3c816a27c0bd45471... [2] https://github.com/digama0/oleandump [3] https://github.com/ammkrn/nanoda_lib