@article{GDZPPN002291037,
title = {Classical Differential Invariants and Applications to Partial Differential Equations.},
journal = {Mathematische Annalen},
volume = {146},
year = {1962},
pages = {308-329},
zbl = {0171.06301},
url = {http://dml.mathdoc.fr/item/GDZPPN002291037}
}
JOHNSON, H.H. Classical Differential Invariants and Applications to Partial Differential Equations.. Mathematische Annalen, Tome 146 (1962) pp. 308-329. http://gdmltest.u-ga.fr/item/GDZPPN002291037/