@article{DAN_1989_307_4_a5,
     author = {V. A. Kostin},
     title = {Analytic semigroups and cosine functions},
     journal = {Doklady Akademii Nauk},
     pages = {796--799},
     publisher = {mathdoc},
     volume = {307},
     number = {4},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_307_4_a5/}
}