A search of this site, http://tex.stackexchange.com/search?q=%5Cetalchar+ reveals that the command \etalchar
exists already for use in bibliography applications. It is defined, for example, in the alphadin.bst
file (https://github.com/youkan/abschlussarbeit-latex/blob/master/alphadin.bst)
If the OP was not himself defining the command explicitly, it could mean that there is a package conflict, in which two separate packages are both trying to define the macro \etalchar
.
However, based on the comment from the OP, it appears that a redundant call was accidentally made to the bibliography, which had the effect of trying to execute the same set of code twice, containing the \etalchar
definition. Thus, an error was thrown, as a result of the redundancy.
Relevant part of alphadin.bst
code:
FUNCTION {begin.bib}
{ et.al.char.used
{ "\newcommand{\etalchar}[1]{$^{#1}$}" write$ newline$ }
'skip$
if$
preamble$ empty$
'skip$
{ preamble$ write$ newline$ }
if$
"\begin{thebibliography}{" longest.label * "}" * write$ newline$
newline$
"% this bibliography is generated by alphadin.bst [8.2] from 2005-12-21"
write$ newline$
newline$
"\providecommand{\url}[1]{\texttt{#1}}"
write$ newline$
"\expandafter\ifx\csname urlstyle\endcsname\relax"
write$ newline$
" \providecommand{\doi}[1]{doi: #1}\else"
write$ newline$
" \providecommand{\doi}{doi: \begingroup \urlstyle{rm}\Url}\fi"
write$ newline$
}
alphadin.bst
file (github.com/youkan/abschlussarbeit-latex/blob/master/…)