\expandafter\xdef\csname c@tcode\endcsname{\the\catcode`\@}
\catcode`\@=11
%
\newdimen\leftm@rgin   \leftm@rgin=1.5in
\newdimen\rightm@rgin  \rightm@rgin=1in
\newdimen\topm@rgin    \topm@rgin=1in
\newdimen\bottomm@rgin \bottomm@rgin=1in
\newdimen\p@perheight  \p@perheight=11in
\newdimen\p@perwidth   \p@perwidth=8.5in
%
\def\leftmargin{\afterassignment\setmargins\leftm@rgin}
\def\rightmargin{\afterassignment\setmargins\rightm@rgin}
\def\topmargin{\afterassignment\setmargins\topm@rgin}
\def\bottommargin{\afterassignment\setmargins\bottomm@rgin}
%
\def\setmargins{%
\dimen255=\leftm@rgin \advance\dimen255 by -1in \hoffset=\dimen255
\dimen255=\p@perwidth \advance\dimen255 by -\rightm@rgin 
\advance\dimen255 by -\leftm@rgin \hsize=\dimen255
\dimen255=\topm@rgin \advance\dimen255 by -1in \voffset=\dimen255
\dimen255=\p@perheight \advance\dimen255 by -\bottomm@rgin 
\advance\dimen255 by -\topm@rgin \vsize=\dimen255}
%
\def\tr@emargins{}
\def\landscape{\p@perheight=8.5in \p@perwidth=11in \setmargins}
%\def\afour{\p@perheight=?cm \p@perwidth=?cm \setmargins}
%
\catcode`\@=\c@tcode