[tehwalrus]

So, you write down the formal requirements you have of an operating system (with aggressive auto-updates enabled, or disabled, as the customer chooses) once, on a piece of paper, and hope that they don't change?

Your method seems impractical in the extreme in a commercial team environment.

[catnaroek]

I don't need to “hope” for anything. All I have to do is document the program's preconditions.