The three rules of the Librarians of Time and Space are: 1) Silence; 2) Books must be returned by no later than the date shown; and 3) Do not interfere with the nature of causality.
Terry PratchettYOU MUST LEARN THE COMPASSION PROPER TO YOUR TRADE" "And what's that?" "A SHARP EDGE.
Terry PratchettThe Library didn't only contain magical books, the ones which are chained to their shelves and are very dangerous. It also contained perfectly ordinary books, printed on commonplace paper in mundane ink. It would be a mistake to think that they weren't also dangerous, just because reading them didn't make fireworks go off in the sky. Reading them sometimes did the more dangeous trick of making fireworks go off in the privacy of the reader's brain.
Terry Pratchett