@article{TIMM_2011_17_3_a13,
     author = {M. V. Deikalova},
     title = {Several extremal approximation problems for the characteristic function of a~spherical layer},
     journal = {Trudy Instituta matematiki i mehaniki},
     pages = {122--135},
     publisher = {mathdoc},
     volume = {17},
     number = {3},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMM_2011_17_3_a13/}
}