@article{DAN_1958_118_2_a6,
     author = {S. G. Krein and P. E. Sobolevskii},
     title = {Differential equation with abstract elliptical operator in {Hilbert} space},
     journal = {Doklady Akademii Nauk},
     pages = {233--236},
     publisher = {mathdoc},
     volume = {118},
     number = {2},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_118_2_a6/}
}