@article{TM_2019_304_a2,
     author = {A. A. Agrachev},
     title = {Spectrum of the {Second} {Variation}},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {32--48},
     publisher = {mathdoc},
     volume = {304},
     year = {2019},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_2019_304_a2/}
}