1. Wigner E.: Symmetries and Reflections. Indiana University Press, Bloomington, IN (1967)
2. Bochner, S.: The Role of Mathematics in the Rise of Science, 4th edn. Princeton University Press, Princeton, NJ (1981). See p.v (Preface). The first edition was written in the mid sixties
3. London Philosophy Study Guide, University of London, http://www.ucl.ac.uk/philosophy/LPSG/Ch22.pdf . NB Do not google the acronym LPSG to find the site
4. Neugebauer O.: The Exact Sciences in Antiquity, 2nd edn. Dover Publications, New York (1969)
5. Allen, D.: Pythagoras and the Pythagoreans. http://www.math.tamu.edu/~dallen/history/pythag/pythag.html (1997)