@article{DE_1975_11_2_a21,
     author = {A. A. Levakov},
     title = {On sufficient optimality conditions},
     journal = {Differencialʹnye uravneni\^a},
     pages = {385--387},
     publisher = {mathdoc},
     volume = {11},
     number = {2},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1975_11_2_a21/}
}