“[T]he concept of control is seen to be role based – that is, which part of a linked feedback system is the controller and which the controlled is not clear-cut, but depends on a point of view. In traditional terms, the thermostat controls the heating system. But what controls the thermostat, making it switch state? The answer, of course, is the ambient temperature – which is a (nonexclusive) product of the heating system. In this respect, the heating system at least partially controls the thermostat.”