@article{100157,
author = {Otomar H\'ajek},
title = {Funktsional'nye uravneniia trigonometricheskikh funktsii},
journal = {Czechoslovak Mathematical Journal},
volume = {05},
year = {1955},
pages = {432-434},
zbl = {0068.32004},
mrnumber = {0089358},
language = {ru},
url = {http://dml.mathdoc.fr/item/100157}
}
Hájek, Otomar. Функциональные уравнения тригонометрических функций. Czechoslovak Mathematical Journal, Tome 05 (1955) pp. 432-434. http://gdmltest.u-ga.fr/item/100157/