Whether or not the actual machine really does what I'm about to tell you is completely irrelevant at this moment. In fact, this is an engineering model, in the same way that, [for an] electrical resistor, we write down a model V = IR — it's approximately true, but it's not really true; if I put enough current through the resistor, it goes boom, so the voltage is not always proportional to the current, but for some purposes the model is appropriate. In particular, the model we're going to describe right now, which I call the substitution model, is the simplest model that we have for understanding how procedures work and how processes work — how procedures yield processes.