@article{DAN_1984_276_1_a11,
     author = {S. S. Shterengas},
     title = {Riesz summation and the operator cosine-function},
     journal = {Doklady Akademii Nauk},
     pages = {51--54},
     year = {1984},
     volume = {276},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1984_276_1_a11/}
}