\catcode`\{=1 % left brace is begin-group character
\catcode`\}=2 % right brace is end-group character
\catcode`\#=6 % hash mark is macro parameter character
%
\let\x=\input \def\input#1 {\let\input=\x \let\x=\undefined}
%
\let\qayb=\font
\def\font#1=#2 {\def\qayba{#1}\def\qaybb{#2}
                \def\qaybf{\preloaded}
                \def\qaybg{\tenrm}\def\qaybh{\tenex}
                \def\qaybu{cmr7}\def\qaybv{cmtt10}\def\qaybw{cmssbx10}
                \ifx\qayba\qaybg \qayb#1=#2
                \else\ifx\qayba\qaybh \qayb#1=#2
                \else\ifx\qayba\qaybf
                  \ifx\qaybb\qaybu \qayb#1=#2
                  \else\ifx\qaybb\qaybv \qayb#1=#2
                  \else\ifx\qaybb\qaybw \qayb#1=#2 \fi\fi\fi
                \fi\fi\fi}
%
\let\qayc=\skewchar \def\skewchar#1=#2 {\relax}
\let\qayd=\textfont \def\textfont#1=#2{\relax}
\let\qaye=\scriptfont \def\scriptfont#1=#2{\relax}
\let\qayf=\scriptscriptfont \def\scriptscriptfont#1=#2{\relax}
%
\x plain
%
\let\font=\qayb \let\qayb=\undefined
\let\skewchar=\qayc  \let\qayc=\undefined
\let\textfont=\qayd  \let\qayd=\undefined
\let\scriptfont=\qaye  \let\qaye=\undefined
\let\scriptscriptfont=\qayf  \let\qayf=\undefined
%
