@article{MZM_2015_97_2_a14,
     author = {I. N. Braeutigam and K. A. Mirzoev and T. A. Safonova},
     title = {An {Analog} of {Orlov's} {Theorem} on the {Deficiency} {Index} of {Second-Order} {Differential} {Operators}},
     journal = {Matemati\v{c}eskie zametki},
     pages = {314--317},
     publisher = {mathdoc},
     volume = {97},
     number = {2},
     year = {2015},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_2015_97_2_a14/}
}