(see paragraph 28)

In my paper writing, I put wikilinks around things that I want to follow up on. They stand out visually when you scan back over something afterwards.

One more thing ought to be explained in advance: why the card index is indeed a paper machine. As we will see, card indexes not only possess all the basic logical elements of the universal discrete machine — they also fi t a strict understanding of theoretical kinematics . The possibility of rear-ranging its elements makes the card index a machine: if changing the position of a slip of paper and subsequently introducing it in another place means shifting other index cards, this process can be described as a chained mechanism. This “ starts moving when force is exerted on one of its movable parts, thus changing its position. What follows is mechanical work taking place under particular conditions. This is what we call a machine . ” 11 The force taking effect is the user ’ s hand. A book lacks this property of free motion, and owing to its rigid form it is not a paper machine.