Due to legibility constraints, it has not been possible to indicate explicitly the technical source of each fact reported in the preceding chapters. However, I have carefully kept track of all the sources in my notes, so if you need to know where I found a specific item of information, just e-mail me at paolo.attivissimo@gmail.com.
The main reference sources are listed in the following pages and are also useful as further reading on the subject. Many are available directly on the Internet: for the sake of brevity, I have not included links to all of them.
