Set Theory in mathematics uses Venn Diagrams like this one to depict the
proofs of theorems.
If you haven't already done so, first
download the
free trial version of RFFlow. It will allow you to open any chart and make
modifications.
Once RFFlow is installed, you can open the above chart in RFFlow by clicking
on
Venn_Diagram.flo.
From there you can zoom in, edit, and print this sample chart. It is often
easier to modify an existing chart than to draw it from scratch.
To draw this chart without downloading it, run RFFlow and click on the
More
Shapes 
button, click the
Circles stencil, and
then click the
Add Stencil button.