@article{TMF_1989_80_3_a11,
     author = {I. A. Vakarchuk},
     title = {Density matrices of~superfluid {helium-4.~I}},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {439--451},
     publisher = {mathdoc},
     volume = {80},
     number = {3},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1989_80_3_a11/}
}