@article{DE_1969_5_7_a15,
     author = {G. N. Yakovlev},
     title = {A certain variational problem},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1303--1312},
     publisher = {mathdoc},
     volume = {5},
     number = {7},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_7_a15/}
}