1. Invariante variationsprobleme. Nachr. König. Gesell. Wissen., Göttingen;Noether;Math Phys Kl Heft,1918
2. Über die erhaltungssätze der elektrodynamik;Bessel-Hagen;Math Ann,1921
3. Symmetries and differential equations;Bluman,1989
4. Application of Lie groups to differential equations;Olver,1993
5. Group analysis of differential equations;Ovsiannikov,1982