@article{DE_1991_27_5_a0,
     author = {E. R. Avakov},
     title = {First-order necessary conditions for abnormal problems in the calculus of variations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {739--745},
     year = {1991},
     volume = {27},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1991_27_5_a0/}
}