One of the touted advantages of formal methods is the ability to do proof. But examples of
proofs as part of industrial formal methods projects are relatively hard to find. I describe here
two of the large Z proof projects I have been involved in at Logica, and show how the entire
specification and proof process is deeply affected by why something is being proved, what is
being proved, and how the finished proof is to be presented. I finish off by describing, based
on my experiences, what I believe to be the requirements for an industrial-strength Z proof …