1. In the following, frequent references will be made to the following three sources: E P Wigner, Group Theory and its Application to the Quantum Mechanics of Atomic Spectra, Academic Press, New York, 1959
2. Reviews of Modern Physics, Vol.34, No.4, 1962
3. E P Wigner, Symmetries and Reflections — Scientific Essays, Indiana University Press, 1967. For brevity we shall refer to these as GT, RMP and SR, respectively.
4. SR, p. 257.
5. E P Wigner, Remembering Paul Dirac, in Reminiscences about a Great Physicist: Paul Adrien Maurice Dirac, (eds. B N Kursunoglu and E P Wigner), Cambridge University Press, Cambridge, 1987.