The Feyman Lectures on Physics, Ed. Addison Wesley, Vol. 1, cap. 52, (1964),
M. I. Petrashen, E. D. Trifonov; Applications of Group Theory
in Quantum Mechanics, The M.I.T. Press, pág. 3-12,
(1969).
I. Tamm, Z,. Physik 71, 141 (1931).
M. Fierz, Helv. Phys. Acta 17, 27 (1944).
P. A. M. Dirac, Phys. Rev. 78, 817 (1948).
D. Zwanziger, Phys. Rev. 3, 880 (1971); 176, 1489 (1968).
D. T. Miller, Proc. Camb. Phil. Soc. 69, 449 (1971).