@article{DAN_1994_336_5_a1,
     author = {V. A. Kostin},
     title = {On the solution of a problem associated with an abstract cosine},
     journal = {Doklady Akademii Nauk},
     pages = {584--586},
     publisher = {mathdoc},
     volume = {336},
     number = {5},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1994_336_5_a1/}
}