@article{DAN_1991_317_2_a1,
     author = {N. A. Bobylev and Yu. M. Burman},
     title = {Morse lemmas for integral functionals},
     journal = {Doklady Akademii Nauk},
     pages = {267--270},
     year = {1991},
     volume = {317},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_317_2_a1/}
}