@article{TMF_1969_1_2_a11,
     author = {M. M. Mestechkin},
     title = {Conditions for the representability of the density matrix},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {287--294},
     year = {1969},
     volume = {1},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1969_1_2_a11/}
}