V10/vol2/index/X

\def\makeindex{\if@filesw \newwrite\@indexfile
  \immediate\openout\@indexfile=\jobname.idx
  \def\index{\@bsphack\begingroup
             \def\protect####1{\string####1\space}\@sanitize
             \@wrindex\@indexfile}\typeout
  {Writing index file \jobname.idx }\fi}

\def\@wrindex#1#2{\let\thepage\relax
   \xdef\@gtempa{\write#1{\string
      \indexentry{#2}{\thepage}}}\endgroup\@gtempa
   \if@nobreak \ifvmode\nobreak\fi\fi\@esphack}

\def\index{\@bsphack\begingroup \@sanitize\@index}

\def\@index#1{\endgroup\@esphack}