"If you've been to a science fiction convention you have likely encountered The Wall of Books. You go into a panel on, say, "Using Historical Plumbing in Outer Space Settings" hoping to pick up some useful reference data. There are five people sitting on the panel-or rather, there are four people and one Wall of Books. One presumes there's a person behind the Wall of Books, but the wall is so high and so impenetrable that one cannot be sure. And you know from the Wall of Books that the panelist isn't really there to talk about Thomas Crapper or the use of logs in sewer systems-she's there to display her books in the hopes that people will buy them."
