Out of interest, how close are formal methods to the mathematical standard for proofs? VDM-SL was part of my degree, but the lecturer ended up showing more limitations than strengths by getting his own example wrong, and sadly I've had no real-life experience with them because none of my career to date has involved things that need to be proven correct.

That's shifting the goal post. But sure, jesuslop's pointer to the Curry-Howard-correspondance is closer to the meat.