Copyright (C) Jeffrey Elkner, Allen B. Downey and Chris Meyers.
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 Foreward, Preface, 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”.