@article{DAN_1976_228_2_a0,
     author = {V. G. Boltyanskii},
     title = {Generalization of a theorem of {B.~Sz.-Nagy}},
     journal = {Doklady Akademii Nauk},
     pages = {265--268},
     publisher = {mathdoc},
     volume = {228},
     number = {2},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1976_228_2_a0/}
}