1. Elliot, J., Dawber, P.: Symmetry in Physics. New York: Oxford University Press, 1979
2. Gourdin, M.: Lagrangian Formalism and Symmetry Laws. New York: Gordon and Breach, 1969
3. Olver, P.: Applications of Lie Groups to Differential Equations. Berlin, Heidelberg, New York: Springer, 1993
4. Bluman, G., Kumei, S.: Symmetries of Differential Equations. Berlin, Heidelberg, New York: Springer, 1989
5. Noether, E.: Nachr. Konig. Gesell. Wissen. Gottinger Math. Phys. Kl., 235 (1918)