\def{text F=\parm1}
\def{text f=item(1,\F)}
\def{text g=item(2,\F)}
\def{text a=item(3,\F)}
\def{text b=item(4,\F)}
\def{real tt=\a}
\def{real xxv=evalue(\f,t=\tt)}
\def{real yyv=evalue(\g,t=\tt)}
\def{real maxx=\xxv}
\def{real minx=\xxv}
\def{real maxy=\yyv}
\def{real miny=\yyv}
\def{text nn=\parm3}
\for{i=1 to \nn}
{\def{real tt=\a+\i*(\b-(\a))/(\nn)}
\def{real xx=evalue(\f,t=\tt)}
\def{real yy=evalue(\g,t=\tt)}
\def{real minx=min(\minx,\xx)}
\def{real maxx=max(\maxx,\xx)}
\def{real miny=min(\miny,\yy)}
\def{real maxy=max(\maxy,\yy)}
}
\def{real xsize1=\minx-1.2}
\def{real xsize2= \maxx +1.2}
\def{real ysize1= \miny-1}
\def{text ysize2= \maxy+0.5}
\def{real prop=  (\ysize2-(\ysize1))/(\xsize2-(\xsize1))}