@article{RM_1961_16_4_a19,
     author = {P. E. Sobolevskii},
     title = {On logarithms of normal positive operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {16},
     number = {4},
     year = {1961},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1961_16_4_a19/}
}