1. Similarity Methods for Differential Equations;Bluman,1974
2. The Group Analysis of Differential Equations;Ovsiannikov,1978
3. Applications of Lie Groups to Differential Equations;Olver,1986
4. Symmetries and Differential Equations;Bluman,1989
5. Symmetry Analysis and Exact Solutions of Equations of Non-linear Mathematical Physics;Fushchych,1993