This is the second in a series of a few short books about the foundations of quantum field theory.
We would like to acknowledge here the contribution to parts of the
material contained within this book by former students and collaborators
who were active in this subject in the past: Dr. Timothy Edward Gallivan
and Dr. André Cavalcanti Rocha Martins. When appropriate, due credit
will be given in footnotes along the text. We would also like to thank
those that helped by reading and correcting the manuscript at various
stages of its production.