LуkоvаОВ. Extension of a theorem of N. N. Bogolyubov to the case of a Hilbert space . Ukr. Mat. Zhurn. [Internet]. 1966Aug.31 [cited 2024Nov.24];18(5):53-9. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/8440