1. Landau, L.D., Lifshits, E.M.: Quantum Mechanics, 3rd edn. Nauka, Moscow (1974). Ch.12 (in Russian)
2. Pikin, S.A.: Structural Transformations in Liquid Crystals. Gordon & Breach, New York (1991)
3. Sonin, A.S.: Besedy o kristallofizike (Talks on Crystal Physics). Atomizdat, Moscow (1976) (in Russian)
4. Hargittai I., Hargittai, M.: Symmetry Through the Eyes of a Chemist. VCH Verlaggesellschaft, New York (1986)
5. Bhagavantam, S., Venkatarayudu, T.: Theory of Groups and Its Applications to Physical Problems, 2nd edn. Andhra University, Waltair (1951)