1. E. P. Wigner, in Group Theoretical Concepts and Methods in Elementary Particle Physics (Ed. F. Gursey), Gordon & Breach, New York, 1964, p. 37.
2. E. Artin, Geometric Algebra, Academic Press, New York, 1951, p. 88.
3. Proofs of the Wigner theorem can be found in Ludwig, (1954), p. 101; U. Uhlhorn, Ark. Fys.
23, 307 (1963) ;
4. L. O’Raifeartaigh, G. Rasche, Ann. of Phys.
25, 155 (1963) ;
5. V. Bargmann, Ann. of Math.
59, 1 (1954).