I'd like to thank you all for the help.
I'd like to ask, what is the `phylosophy' of using <text-settings>
and <math-settings> in a \DeclareFontEncoding command?
Do these settings remain globally defined after changing the encoding?
If so, may be it would be good to provive additional arguments
to \DeclareFontEncoding, like <restore-text-settings> and

David Carlisle wrote:

> \DeclareTextSymbol{\CYRV}{LCY}{198}

BTW, why not to write \DeclareTextSymbol\CYRV{LCY}{198}, i.e. without
unnecessary braces?
I do not like to type unnecessary characters in my texts. :-)

With best regards,