the "paracol" package when I give it to install appears the following message "File` paracol.sty 'not found. " Maybe I'm making some mistake but I do not detect it.
\documentclass{letter}
\usepackage{paracol}
\begin{document}
\columnratio{0.6}
\begin{paracol}{2}
\begin{leftcolumn}
The environment may also be restarted
anywhere you like as shown here. ...
\end{leftcolumn}
\begin{rightcolumn}
source
\end{rightcolumn}
\end{paracol}
Now the aurthor will do ...
\end{document}
paracol
from CTAN instead (it's not down).