@article{DAN_1981_261_4_a3,
     author = {G. A. Isaev},
     title = {On the theory of defect indices for multiparameter differential operators of {Sturm{\textendash}Liouville} type},
     journal = {Doklady Akademii Nauk},
     pages = {788--791},
     year = {1981},
     volume = {261},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1981_261_4_a3/}
}