1. S. Sternberg, Lectures on Differential Geometry, Prentice Hall, Englewood Cliffs, N. J. (1964).
2. A. E. Tumanov, "Geometry of CR-manifolds," in: Progress in Science and Technology. Current Problems of Mathematics. Fundamental Directions [in Russian], Vol. 9, Vsesoyuz. Inst. Nauch. Tekh. Informatsii, Moscow (1986), pp. 225?246.
3. E. Bedford and J. Dadok, Comm. Math. Helv.,62, 561?572 (1987).
4. R. Saerens and W. R. Zame, Trans. Am. Math. Soc.,301, No. 1, 413?429 (1987).