@article{DAN_1977_235_4_a6,
     author = {A. Dzhuraev and \`E. Muhamadiev},
     title = {On the normal solvability and index of first-order systems of composite type},
     journal = {Doklady Akademii Nauk},
     pages = {753--756},
     publisher = {mathdoc},
     volume = {235},
     number = {4},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_235_4_a6/}
}