Hi, the indicator wasn't in the diagram because it didn't link up to anything else. It was essentially context setting up the fact the we have these censors, and it eliminates the possibility of uncensored books. The meat of the passage here is the fact that we have two censors with different rates of rejection. The first rejected half, and the second rejected a quarter, and we know that the total number of books not rejected were equal. From there we can basically set up a quick equation to see what else we know about them.
