more abstract Sendback operations, with explicit id/exec_id properties;
purge result messages (again), cf. db58490a68ac, 7b61a539721e;
\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|)}