Latex answers package and cyrilic symbols in enumerate environment

Question

I'm using both the answers package for an exercise book and Cyrillic symbols for 2nd level items. Here is my .tex code.

\documentclass[10pt, a4paper, openany]{report}
\usepackage[utf8]{inputenc}
\usepackage[russian]{babel}
\usepackage{answers}

\begin{document}

\renewcommand{\theenumii}{\asbuk{enumii}}

\Newassociation{otv}{Otvet}{ans}
\Opensolutionfile{ans}[C1.ans6]

\begin{enumerate}
    \item 
        \begin{enumerate}
            \item Excercise 1a)
                \begin{otv}
                    answer 1a)  \end{otv}
            \item Excercise 1b)
                \begin{otv}
                    answer 1a)  \end{otv}
        \end{enumerate}
\end{enumerate}

\Closesolutionfile{ans}

Answers:
\input{c1.ans6}

\end{document}

and this error occurs

...\c1.ans6.tex:1: Undefined control sequence. [\begin{Otvet}{1.1.\T2A\cyra )}]

Answers file contains the following:

\begin{Otvet}{1\T2A\cyra }
                answer 1a)  
\end{Otvet}
\begin{Otvet}{1\T2A\cyrb }
                answer 1a)  
\end{Otvet}

Could anyone help me to deal with this problem?

Answer 1

You need an \immediate version of \protected@write, because commands such as \cyra, produced by \asbuk don't survive \write.

The code is like in Replacing some macro tokens in a list before \write ing, then I also patch \Newassociation to use \protected@iwrite instead of \immediate\write.

\documentclass[10pt, a4paper, openany]{report}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[russian]{babel}
\usepackage{answers}
\usepackage{xpatch}
\makeatletter
% get a copy of `\protected@write
\let\protected@iwrite\protected@write
% patch the copy to add \immediate
\xpatchcmd{\protected@iwrite}{\write}{\immediate\write}{}{}

\xpatchcmd{\Newassociation}
  {\immediate\write\@nameuse{#3@file}}
  {\protected@iwrite{\@nameuse{#3@file}}{}}
  {}{}
\makeatother

\begin{document}

\renewcommand{\theenumii}{\asbuk{enumii}}

\Newassociation{otv}{Otvet}{ans}
\Opensolutionfile{ans}[\jobname.ans6]

\begin{enumerate}
\item 
  \begin{enumerate}
  \item Excercise 1a)
    \begin{otv}
    answer 1a)
    \end{otv}
  \item Excercise 1b)
    \begin{otv}
    answer 1b)
    \end{otv}
  \end{enumerate}
\end{enumerate}

\Closesolutionfile{ans}

Answers:
\input{\jobname.ans6}

\end{document}