$\forall$$T$:Type, $l$:IdLnk, ${\it tg}$:Id, $L$:MsgA List. ($\forall$$M$$\in$$L$. $T$ $\subseteq\rho$ $M$.din($l$,${\it tg}$)) $\Rightarrow$ $T$ $\subseteq\rho$ $\oplus$($L$).din($l$,${\it tg}$)