more robust range on preceding comment-line;
no range for blank lines;
avoid recursive output_text/mark_range;
clarified Latex.output_token (no range) vs. Thy_Output.present_token (with range);
\index{model checking example|(}%
\index{lfp@{\texttt{lfp}}!applications of|see{CTL}}
\input{Base.tex}
\input{PDL.tex}
\input{CTL.tex}
\index{model checking example|)}