@article{TM_1990_184_a4,
     author = {V. N. Popov and S. A. Fedotov},
     title = {The diagram technique for ferromagnetic systems with spin 1/2},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {159--169},
     publisher = {mathdoc},
     volume = {184},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1990_184_a4/}
}