transparent layer?

["Luis A Escobar" <luis lsu edu>]

I am new to Dia. I have three questions

  1) Other than the documentation included in the distribution
  is there a book with example to learn to use the system?

  2) Does anybody know of a site where I can see Dia used
      to illustrate set operations (unions, intercepts, complements, etc)?

  3)  I want to overlap two elipses and see the hidden boundary of the
       ellipse that is on the bottom. What is the process to get it done?
       Some kind of transparent layer?

       I have overlapped the elipses but I can't see the boundary of the
       one at the bottom.

Thank you

 Luis A. Escobar