The fonts ‘\indextt’, ‘\indexrm’ are used in indexes, and they are introduced with the command \IndexFonts.
<..indexes..>+
\ifx \IndexFonts\:UnDef
\def\IndexFonts{%
\setbox\strutbox=\hbox{\vrule height8.0pt depth3.0pt width0pt}
\font\ninerm=cmr9 \font\ninebf=cmbx9 \font\ninesl=cmsl9
\font\nineit=cmti9 \font\ninett=cmtt9 \font\ninei =cmmi9
\font\ninesy=cmsy9 \font\nineex=cmex10
\textfont0=\ninerm \textfont1=\ninei \textfont2=\ninesy
\textfont3=\nineex \scriptfont3=\nineex \scriptscriptfont3=\nineex
\textfont\bffam=\ninebf \textfont\slfam=\ninesl
\textfont\itfam=\ninei \textfont\ttfam=\ninett
\def\rm{\fam=0 \ninerm}%
\def\bf{\fam=\bffam\ninebf}%
\def\sl{\fam=\slfam\ninesl}%
\def\it{\fam=\itfam\nineit}%
\def\tt{\fam=\ttfam\ninett}%
\def\cal{\fam=2}%
\def\mit{\fam=1}%
\skewchar\ninei =127 \skewchar\ninesy =46 \rm
\baselineskip=11pt }
\fi
-_-_-