1. Ovsyannikov, L.V., Group Analysis of Differential Equations, Academic Press, New York, 1982.
2. Ibragimov, N.H., Transformation Groups Applied to Mathematical Physics, Reidel, Dordrecht, 1985.
3. Olver, P.J., Application of Lie Groups to Differential Equations, Springer-Verlag, New York, 1986.
4. Noether, E., Invariante Variationsprobleme, Nachr. Konig. Gesell. Wissen. Göttingen, Math.-Phys. Kl., 1918, pp. 235–257.
5. Dorodnitsyn, V.A., Taylor’s group and transformations conserving finite-difference derivatives, Keldysh Inst. Appl. Mathem., Preprint N. 67, 1987, pp. 1–31, (in Russian).