\PGset[0.7em]
\begin{picture}   (40, 10)

\drawline     ( 1, 1)( 7, 1)( 7, 7)( 1, 7)( 1, 1) % R
\drawline     (11, 1)(18, 1)(18, 8)(11, 8)(11, 1) % R'

\dashline[80]{0.4}(31, 1)(39, 1)(39, 9)(31, 9)(31, 1) % S

\dashline[80]{0.2}(21, 8)(21, 1)(29, 1) % BAC
\dashline[80]{0.2}(21, 6)(27, 1)

\put(  3.5  , 3.5 ) {$\scriptstyle R$}
\put(  14  ,  4 ) {$\scriptstyle R'$}

\put( 20.1, 5.5 ) {$\scriptstyle B$}
\put( 20.1, .7 ) {$\scriptstyle A$}
\put( 26.5, .2 ) {$\scriptstyle C$}

\put( 34.5, 4.5 ) {$\scriptstyle S$}

\end{picture}
\PGrestore