1. E. Inönü and E. P. Wigner, “On the Contraction of Groups and Their Representations,” Proc. Natl. Acad. Sci. U. S. A. 39, 510–524 (1953).
2. V. A. Rubakov, Classical Gauge Fields (URSS, Moscow, 1999) [in Russian].
3. L. B. Okun’, Leptons and Quarks (URSS, Moscow, 2005) [in Russian].
4. M. E. Peskin and D. V. Schroeder, An Introduction to Quantum Field Theory (Addison-Wesley, New York, 1995).
5. N. A. Gromov, “Possible Contractions of SU(2) Group,” Proc. Komi Sci. Center Ural Branch Russ. Acad. Sci. 1(5), 5–10 (2010).