Logic texts use simple diagrams called Venn diagrams. They have
overlapping circles as components, with parts of the circles filled
in, to illustrate different relations between sets.

If I put two overlapping circles on a Visio diagram, I can fill in
both circles with the same pattern. This illustrates the union of two
sets.

To illustrate the intersection, I need to fill in just the area where
the two circles overlap. This area is not a separate Visio shape, so
I'm having trouble figuring out how to do this. I thought maybe I
could give complementary fills to the two circles somehow, so that the
fill would only be visible in the intersection, but haven't found
anything that works.

Anybody know a Visio trick to solve this problem?

Thanks.

Mike Carroll