@article{FAA_1991_25_3_a0,
     author = {N. A. Bobylev and Yu. M. Burman},
     title = {Morse lemma for functionals of variational calculus},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {1--11},
     publisher = {mathdoc},
     volume = {25},
     number = {3},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_1991_25_3_a0/}
}