$\forall$$A$:Type, $x$:($A$$\rightarrow$$A$$\rightarrow$$A$), $e$:$A$, $S$:Type, $f$:($A$$\rightarrow$$S$$\rightarrow$$S$). IsAction($A$;$x$;$e$;$S$;$f$) $\in$ $\mathbb{P}$