The problem considered in this preprint was suggested by Nikolay Bogolyubov , who advised Boris Struminsky in this research .
Boris Struminsky was a PhD student of Nikolay Bogolyubov .
The problem considered in this preprint was suggested by Nikolay Bogolyubov , who advised PhD student   in this research .
Boris Struminsky was a PhD student of Nikolay Bogolyubov .