This is a Free work. You can redistribute and/or modify it under the terms of either of the following licenses:

• The GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version

• The Free Art License as published by Copyleft Attitude; either version 1.3, or (at your option) any later version

• The Creative Commons Attribution-ShareAlike License as published by Creative Commons; either version 4.0, or (at your option) any later version

• The GNU Free Documentation License as published by the Free Software Foundation; either version 1.3, or (at your option) any later version; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts