@article{DAN_1992_324_1_a2,
     author = {V. V. Ditkin},
     title = {On the root subspaces of a two-parameter spectral problem},
     journal = {Doklady Akademii Nauk},
     pages = {20--23},
     year = {1992},
     volume = {324},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1992_324_1_a2/}
}