[pstricks] Defining a maxmum and minimum point

[Arne Hallam]

So I was looking for an example of the something like the following for 
me to use in class.

I have something I drew in Mathamatica but I ended up using a square for 
a  circular neighborhood because I don't know how to draw implicit 
circles in 3D Mathematica.  So I am now trying PSTricks which works for 
lots of other cool things.


Show a surface in 3 dimensions (which I can easily do).

Show a small circle or disc at (x1,x2,0) in the x1-x2 plane(which I 
cannot do)

Show the points on the surface that lie above this disc (which I am not 
sure how to do, I know how to patch it on top of the first surface in 
different color, but that is about all)

Put a point on the surface above the disc that is maximal in set (which 
I can do).

I would like to add some nice lines and things, but I can do that.