To address your specific concerns regarding "learning the maths": that's a bit disingenuous from the people stating it. It is actually logic they are talking about, rooted in the discrete math branch. For seL4 you can actually read the proofs and their conclusions: http://sel4.systems/Info/FAQ/proof.pml. It's a lot of (structural) induction style proofs. That page will be a good starting point and just google around for missing holes as you need.