@article{DE_1968_4_2_a11,
     author = {G. S. Rozenberg},
     title = {On the question of necessary and sufficient conditions for a minimum in variational problems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {290--297},
     year = {1968},
     volume = {4},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_2_a11/}
}