amsproc class, formating \cite command

Question

Using \documentclass{amsproc}, \bibliographystyle{amsplain}.

With \cite{A,B} one gets something like [1, 2]. I would like to decrease the space (for example to thinspace) between 1, and 2. I would appreciate any suggestion to do that simply, i.e., by (re)defining a macro, instead using additional package. But if a package is unavoidable, ok, but which one?

A minimal working example:

\documentclass{amsproc}
\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@article{testa,
  title= "Title A",
  author= "Author A",
  journal= "Journal A",
  pages= "1-2",
  year = "2012"
}
@article{testb,
  title= "Title B",
  author= "Author B",
  journal= "Journal B",
  pages= "2-3",
  year = "2012"
}
\end{filecontents}

\begin{document}

\cite{testa,testb}
\bibliographystyle{amsplain}
\bibliography{\jobname}
\end{document}

Answer 1

Without using additional packages, add the following lines to the preamble of your document:

\makeatletter
\def\@cite#1#2{{%
 \m@th\upshape\mdseries[{\bfseries #1}{\if@tempswa, #2\fi}]}}
\def\@citex[#1]#2{\leavevmode
\let\@citea\@empty
\@cite{\@for\@citeb:=#2\do
{\@citea\def\@citea{,\penalty\@m\,}%
\edef\@citeb{\expandafter\@firstofone\@citeb\@empty}%
\if@filesw\immediate\write\@auxout{\string\citation{\@citeb}}\fi
\@ifundefined{b@\@citeb}{\hbox{\reset@font\bfseries ?}%
\G@refundefinedtrue
\@latex@warning
{Citation `\@citeb' on page \thepage \space undefined}}%
{\@cite@ofmt{\csname b@\@citeb\endcsname}}}}{#1}}
\makeatother

A complete example:

\documentclass{amsproc}
\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@article{testa,
  title= "Title A",
  author= "Author A",
  journal= "Journal A",
  pages= "1-2",
  year = "2012"
}
@article{testb,
  title= "Title B",
  author= "Author B",
  journal= "Journal B",
  pages= "2-3",
  year = "2012"
}
\end{filecontents}

\makeatletter
\def\@cite#1#2{{%
 \m@th\upshape\mdseries[{\bfseries #1}{\if@tempswa, #2\fi}]}}
\def\@citex[#1]#2{\leavevmode
\let\@citea\@empty
\@cite{\@for\@citeb:=#2\do
{\@citea\def\@citea{,\penalty\@m\,}%
\edef\@citeb{\expandafter\@firstofone\@citeb\@empty}%
\if@filesw\immediate\write\@auxout{\string\citation{\@citeb}}\fi
\@ifundefined{b@\@citeb}{\hbox{\reset@font\bfseries ?}%
\G@refundefinedtrue
\@latex@warning
{Citation `\@citeb' on page \thepage \space undefined}}%
{\@cite@ofmt{\csname b@\@citeb\endcsname}}}}{#1}}
\makeatother

\begin{document}

\cite{testa,testb}
\bibliographystyle{amsplain}
\bibliography{\jobname}
\end{document}

The output zoomed to 200%:

Using packages, you can simply load the cite package:

\usepackage{cite}