@article{DAN_1987_292_3_a0,
     author = {N. A. Bobylev},
     title = {A characteristic of extremals of variational problems},
     journal = {Doklady Akademii Nauk},
     pages = {521--524},
     publisher = {mathdoc},
     volume = {292},
     number = {3},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1987_292_3_a0/}
}