"Beware of bugs in the above code; I have only proved it correct, not tried it." - Donald Knuth

Not that relevant in context as the code in question is used to conclude a formal proof, not the other way around. Buy hey, it is a common quote when talking about proving software and someone has to do it...

Context: https://staff.fnwi.uva.nl/p.vanemdeboas/knuthnote.pdf