How to use Cyrillic letter as a mathematical symbol? [duplicate]

Question

I want to use \cyrgup in my document for some derivations. Is there any package that needs to be installed?

Answer 1

Some other fonts. As can be seen here, the command \cyrgup is a mapping to the unicode U+0491 CYRILLIC SMALL LETTER GHE WITH UPTURN. Here are the available fonts and you may fonts installed on your machine to see the possible symbols.

% arara: pdflatex

\documentclass{article}
\usepackage[T2A]{fontenc}
\usepackage{gentium}

\begin{document}
\cyrgup
\end{document}

% arara: lualatex

\documentclass{article}
\usepackage{fontspec}
\newcommand*{\cyrgup}{\symbol{"0491}}

\begin{document}
    \setmainfont{code2000.ttf}
    \cyrgup
    \setmainfont{symbola.ttf}
    \cyrgup
    \setmainfont{quivira.otf}
    \cyrgup
    \setmainfont{EB Garamond}
    \cyrgup
    \setmainfont{Linux Libertine O}
    \cyrgup 
\end{document}

Answer 2

The \cyrgup command is defined in the T2A font encoding (cyrillic and not greek...), so it should suffice to load the package fontenc with that encoding table.

MWE:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1,T2A]{fontenc}

\begin{document}
\cyrgup
\end{document} 

Output