$\forall$$M_{1}$, $M_{2}$:MsgA. $M_{1}$ $\subseteq$ $M_{2}$ $\Rightarrow$ ($\forall$$k$:Knd, $x$:Id. $M_{2}$.frame($k$ affects $x$) $\Rightarrow$ $M_{1}$.frame($k$ affects $x$))