@article{DAN_1970_193_6_a8,
     author = {P. E. Sobolevskii},
     title = {On $S$-numbers of positive operators},
     journal = {Doklady Akademii Nauk},
     pages = {1245--1247},
     publisher = {mathdoc},
     volume = {193},
     number = {6},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_193_6_a8/}
}