Kurgansky, M. V.
Article History
Received: 27 June 2019
Revised: 5 August 2019
Accepted: 25 September 2019
First Online: 12 March 2020
ADDITIONAL INFORMATION
: In 2019, Obukhov’s outstanding work [CitationRef removed] turned 70. The author would be happy if this paper could be published on this anniversary.