1. Über die integration durch bestimmte Integrale von einer Klasse linearer partieller Differential gleichungen;Lie;Arch. Math.,1881
2. Group Analysis of Differential Equations;Ovsiannikov,1982
3. Applications of Lie Groups to Differential Equations;Olver,1986
4. Transformation Groups Applied to Mathematical Physics;Ibragimov,1985
5. Symmetries and Differential Equations;Bluman,1989