@article{DAN_1980_250_3_a6,
     author = {G. A. Isaev},
     title = {On root elements of multiparameter spectral problems},
     journal = {Doklady Akademii Nauk},
     pages = {544--547},
     publisher = {mathdoc},
     volume = {250},
     number = {3},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1980_250_3_a6/}
}