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@article{MS_1980__155_3_a3, author = {{\CYRA}.{\CYRV}. {\CYRS}{\cyra}{\cyrr}{\cyrery}{\cyrch}{\cyre}{\cyrv}}, title = {The index of the second variation of a control system}, journal = {Matemati\v{c}eskij sbornik}, pages = {464--486}, publisher = {mathdoc}, volume = {155}, number = {3}, year = {1980}, zbl = {0484.49012}, language = {en}, url = {http://geodesic.mathdoc.fr/item/MS_1980__155_3_a3/} }
А.В. Сарычев. The index of the second variation of a control system. Matematičeskij sbornik, Tome 155 (1980) no. 3, pp. 464-486. http://geodesic.mathdoc.fr/item/MS_1980__155_3_a3/