@article{RM_1965_20_6_a12,
     author = {N. M. Dobrovol'skaya and V. A. Ponomarev},
     title = {A~pair of counter-operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     year = {1965},
     volume = {20},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1965_20_6_a12/}
}