Command \ch and \arctg already defined

Question

Two errors: document.tex: error: 2: Command \ch already defined. \begin{document} document.tex: error: 2: Command \arctg already defined. \begin{document} for that simple piece of code:

\documentclass[onecolumn]{jetpl}
\begin{document}
\maketitle
\end{document}

JETPL class file is from here: http://jetpletters.ru/tex/utf8/jetpl.cls

Answer 1

The class will always give those errors. It loads babel with the russian option and russianb.ldf will then be loaded which does, amongst other things

    \DeclareMathOperator{\ch}{ch}%\MakeRobust\ch
    \DeclareMathOperator{\tg}{tg}%\MakeRobust\tg
    \DeclareMathOperator{\ctg}{ctg}%\MakeRobust\ctg
    \DeclareMathOperator{\arctg}{arctg}%\MakeRobust\arctg%
    \DeclareMathOperator{\arcctg}{arcctg}%\MakeRobust\arcctg%

but the class itself also does

\DeclareRobustCommand*{\ch}{\myglue\hbox{--}\hskip.167em}

and

\def\arctg{\mathop{\text{arctg}}\nolimits}

You should report this to the class maintainers but the simplest fix is to comment the lines out of the class file (lines 571 and 1241)