@article{DAN_1958_121_6_a3,
     author = {B. R. Lavruk},
     title = {The index of a boundary problem operator for an elliptical system of second order linear differential equations, 
},
     journal = {Doklady Akademii Nauk},
     pages = {970--972},
     publisher = {mathdoc},
     volume = {121},
     number = {6},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_121_6_a3/}
}