Here is the direct link to the PDF version of the second edition published in 1994 (third one published in 2006 is in print though): http://www.math.upenn.edu/

Here is the direct link to the PDF version of the second edition published in 1994 (third one published in 2006 is in print though): http://www.math.upenn.edu/~wilf/gfology2.pdf http://www.math.upenn.edu/~wilf/gfology2.pdf