@article{VTGU_2017_49_a0,
     author = {Ya. V. Borisova and I. A. Kolesnikov and S. A. Kopanev},
     title = {On small variation formulas},
     journal = {Vestnik Tomskogo gosudarstvennogo universiteta. Matematika i mehanika},
     pages = {5--15},
     year = {2017},
     number = {49},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VTGU_2017_49_a0/}
}