This book is Copyright (C) 1999-2015 David A. Wheeler. Permission is granted to copy, distribute and/or modify this book under the terms of the GNU Free Documentation License (GFDL), Version 1.1 or any later version published by the Free Software Foundation; with the invariant sections being “About the Author”, with no Front-Cover Texts, and no Back-Cover texts. A copy of the license is included in the section entitled “GNU Free Documentation License”. This book is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. The image of the Sallet (ca. 1450) is provided by the Walters Art Museum in Baltimore, Maryland, at http://art.thewalters.org/detail/40677/sallet/.