A set of books with the equivalence relation "x and y have the same ISBN number".
<ul><li><a href="//commons.wikimedia.org/wiki/File:Nuvola_apps_bookcase.svg" title="File:Nuvola apps bookcase.svg">Nuvola apps bookcase.svg</a>: Peter Kemp</li>
<li>derivative work: <a rel="nofollow" class="external text" href="http://kulla.me/">Stephan Kulla</a> (<a href="//commons.wikimedia.org/wiki/User:Stephan_Kulla" title="User:Stephan Kulla">Stephan Kulla</a>)</li></ul>
LGPL
<ul><li><a href="//commons.wikimedia.org/wiki/File:Nuvola_apps_bookcase.svg" title="File:Nuvola apps bookcase.svg">Nuvola apps bookcase.svg</a></li></ul>