1. Nonlinear Partial Differential Equations in Engineering, Vol. 2;Ames,1972
2. Group Analysis of Differential Equations;Ovsiannikov,1982
3. Transformation Groups Applied to Mathematical Physics;Ibragimov,1985
4. Applications of Lie Groups to Differential Equations;Olver,1986
5. Symmetries and Differential Equations;Bluman,1989