$\forall$$a$:Id, $T$:Type, ${\it ds}$:$x$:Id fp$\rightarrow$ Type, $P$:(State(${\it ds}$)$\rightarrow$$T$$\rightarrow$Prop), ${\it init}$:$x$:Id fp$\rightarrow$ ${\it ds}$($x$)?Void.
\\[0ex](with ds: ${\it ds}$ init: ${\it init}$action $a$:$T$ precondition $a$(v) is $P$) $\in$ MsgA