@article{DAN_1989_307_4_a2,
     author = {N. A. Bobylev and M. A. Krasnosel'skii},
     title = {Normal deformations of variational problems},
     journal = {Doklady Akademii Nauk},
     pages = {785--788},
     publisher = {mathdoc},
     volume = {307},
     number = {4},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_307_4_a2/}
}