%0 Journal Article %A V. V. Arestov %T Approximation of linear operators, and related extremal problems %J Informatics and Automation %D 1975 %P 29-42 %V 138 %I mathdoc %U http://geodesic.mathdoc.fr/item/TRSPY_1975_138_a1/ %G ru %F TRSPY_1975_138_a1