1. 1. Akivis, M. A.: On the structure of two-component conjugate systems. Tr. Geom. Sem., 1, 7—31 (1966).
2. 2. Akivis, M. A., Rosenfeld B. A.: Eli Cartan (1869—1951). Moscow (2014).
3. 3. Blaschke, V.: Introduction to differential geometry. Moscow (1957).
4. 4. Vagner, V. V.: The theory of the field of local hyperbands. Tr. Semin. Vectorn. Tensorn. Anal., 8, 197—272 (1950).
5. 5. Laptev, G. F.: Differential geometry of imbedded manifolds. Group theoretical method of differential geometric investigations. Tr. Mosk. Mat. Obs., 2, 275—382 (1953).