A very simplified <a href="https://en.wikipedia.org/wiki/Venn_diagram" class="extiw" title="wikipedia:Venn diagram">Venn diagram</a>.  There are circles labeled A, B, and C.<br>Where they intersect, they are labeled AB, AC, BD, and ABC.
<a href="//commons.wikimedia.org/wiki/User_talk:Elecbullet" title="User talk:Elecbullet">Elecbullet</a>
2009-09-27
I made it from scratch, using Inkscape and a text editor