1. Alekseevskiy, D.V., Lychagin, V.V., Vinogradov, A.M.: Fundamental ideas and conceptions of differential geometry. In: Sovremennye Problemy Matematiki. Fundamental’nye Napravleniy. Itogi Nauki i Techniki, vol. 28, pp. 298. VINITI, AN SSSR, Moscow (1988) (in Russian) [English transl.: Encyclopedia of Math. Sciences, vol. 28, pp. 298, Springer, Berlin (1991)]
2. Arnold, V.I.: Advanced Chapters of the Theory of Ordinary Differential Equations. Nauka, Moscow (1978), p. 400 (in Russian)
3. Bernshteyn, I.N., Rozenfel’d, B.I.: Homogeneous spaces of infinite dimensional Lie algebras and characteristic classes of foliations. Usp. Mat. Nauk 28(4), 103–138 (1973) (in Russian)
4. Cartan, E.: Sur les varietes a connexion projective. Bull. Soc. Math. France 52, 205–241 (1924)
5. Chern, S.S.: Projective geometry, contact transformations, and CR-structures. Arch. Math. 38, 1–5 (1982)