$\forall$$x$:Id, $L$:Top, $t$:Type, $x_{1}$:Id, $t_{1}$:Type, $v$:Top.
\\[0ex]$x$ : $t$ $\parallel$ $x_{1}$ : $t_{1}$ $\Rightarrow$ (only members of $L$ affect $x$ :$t$ $\Vert\!+$ $x_{1}$ : $t_{1}$ initially $x_{1}$ = $v$)