clarified "isabelle display" and 'display_drafts': re-use file and program instance, open asynchronously via desktop environment;
\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|)}