1. Dirac P. A. M., The Quantum Theory of the Electron, Proc. R. Soc. London, Ser. A, 117 (1928) 610; The Quantum Theory of the Electron, Part II, Proc. R. Soc. London, Ser. A, 118 (1928) 351.
2. Weyl H., Gruppentheorie und Quantenmechanik, 2nd edition, (1931) p. 234.
3. Wigner E. P., Unitary Representations of the Inhomogeneous Lorentz Group, Ann. Math., 40 (1939) 149.
4. Wick G. C, Wigner E. P. and Wightman A. S., Intrinsic Parity of Elementary Particles, Phys. Rev., 88 (1952) 101.
5. Wigner E. P., Uber die Operation der Zeitumkehr in der Quanten-mechanik, Gött. Nach. (1931) pp. 546–559. Here for the first time an anti-unitary symmetry appears.