[pdonis]

> if a system's behavior can be characterized with a set of equations, use the equations to talk about the behavior

I agree, and I don't think Knuth's quote was saying anything different.

> If you find out that your equations incorrectly or incompletely characterize the system's behavior, Occam's razor requires you to assume that what you need is a better set of equations.

Yes, but you might not have them, and they might not be easy to find. So you might have to face the fact that, now and for the foreseeable future, you might not be able to use your equations to completely predict or characterize the system's behavior, so you need to actually test your code instead of just proving it correct, as Knuth said.