“A good bookshop is just a genteel Black Hole that knows how to read.”

“The truth is that even big collections of ordinary books distort space, as can readily be proved by anyone who has been around a really old-fashioned secondhand bookshop, one that looks as though they were designed by M. Escher on a bad day and has more stairways than storeys and those rows of shelves which end in little doors that are surely too small for a full-sized human to enter. The relevant equation is: Knowledge = power = energy = matter = mass; a good bookshop is just a genteel Black Hole that knows how to read.”

“It is indeed possible to be widely read, as I am, and still have black holes in one's knowledge.”

“Libraries really are wonderful. They're better than bookshops, even. I mean bookshops make a profit on selling you books, but libraries just sit there lending you books quietly out of the goodness of their hearts.”

“This is Sailor Supergirl,” George says. “She knows all about black holes.”

“Do you know how to read?' 'No. It is one of the black arts.' He nodded. 'But a useful one,' he said.”