Acknowledgements
To my wife, who supports me in everything.
To my children and their questions.
To Luis Heriberto Rivas for always being available to my queries and for giving
me access to interesting materials.
To Mercedes Bueto for her corrections and advice.
To my friend Fabian Rodriguez for having an open mind and for his great
knowledge.
To my brother in law Pedro Diez for helping me collate scientific and
astronomical matters.
And to my family and friends who volunteered as readers of the "manuscript" to
help me improve it.
Canen, Alberto