@article{TIMM_2020_26_4_a0,
     author = {V. V. Arestov and R. R. Akopyan},
     title = {Stechkin's problem on the best approximation of an unbounded operator by bounded ones and related problems},
     journal = {Trudy Instituta matematiki i mehaniki},
     pages = {7--31},
     publisher = {mathdoc},
     volume = {26},
     number = {4},
     year = {2020},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMM_2020_26_4_a0/}
}