@article{DAN_1968_183_2_a6,
     author = {N. H. Ibragimov},
     title = {On the group classification of second order differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {274--277},
     publisher = {mathdoc},
     volume = {183},
     number = {2},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_183_2_a6/}
}