@article{DE_1989_25_10_a3,
     author = {V. G. Zadorozhniy},
     title = {Second-order differential equations in variational derivatives},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1679--1683},
     publisher = {mathdoc},
     volume = {25},
     number = {10},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_10_a3/}
}