Copyright (C) Peter Wentworth, Jeffrey Elkner, Allen B. Downey and Chris Meyers.
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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 Foreword, 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”.