Copyright (C) Jeffrey Elkner, Peter Wentworth, Allen B. Downey, Chris
Meyers, and Dario Mitchell. Permission is granted to copy, distribute
and/or modify this document under the terms of the GNU Free Documentation
License, Version 1.3 or any later version published by the Free Software
Foundation; with Invariant Sections being Forward, Prefaces, and
Contributor List, no Front-Cover Texts, and no Back-Cover Texts. A copy of
the license is included in the section entitled “GNU Free Documentation
License”.