@article{DE_1967_3_5_a14,
     author = {A. N. Erugin},
     title = {Families of extremals},
     journal = {Differencialʹnye uravneni\^a},
     pages = {849--851},
     publisher = {mathdoc},
     volume = {3},
     number = {5},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1967_3_5_a14/}
}