1. Olver, P.J. (1986). Applications of Lie Groups to Differential Equations, Springer.
2. Ovsiannikov, L.V. (2014). Group Analysis of Differential Equations, Academic Press.
3. Stephani, H. (1989). Differential Equations: Their Solutions Using Symmetry, Cambridge University Press.
4. Bluman, G.W., and Anco, S.C. (2002). Symmetry and Integration Methods for Differential Equations, Springer.
5. Integrability by quadratures for systems of involutive vector fields;Ukrainian Math. J.,1991