Books/Resources on generating functions I'm currently doing a research on generating functions, but I have only found few books on this topic. Can anyone provide references (if possible, trying to assess the level of math competence required) on generating functions? 
Ideally, what is the context of the referenced book and further details to help to put the book itself in context would be much appreciated.

The book "A = B" which is freely downloadable at http://www.math.upenn.edu/~wilf/AeqB.html.
