Okay so in the sense of Lean’s kernel, we can trust it as long as we understand it. Verifying it cannot be automated therefore, according to the criterion, it must be small so that it can be verified by a human.

Does it not also follow that we should also understand the geometric kernel using a similar criterion or, what I’m trying to understand, is there a mechanism in play in this project that verifies it for us automatically so that we only need to understand the specification and can trust the generated parts?

There are some pointers to answer this question myself that I’m looking into. Neat stuff.