proper import of Main: BNF_Least_Fixpoint does not "contain pretty much everything", especially it lacks the 'value' command, which is defined *after* theory List;
\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|)}