@article{RM_1963_18_4_a9,
     author = {P. N. Knyazev},
     title = {A~necessary and sufficient condition for the comparability of operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {18},
     number = {4},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1963_18_4_a9/}
}