$\forall$$A$:Type, $P$, $Q$:(($A$ List)$\rightarrow$Prop).
\\[0ex]safety($A$;$x$.$P$($x$)) $\Rightarrow$ safety($A$;$x$.$Q$($x$)) $\Rightarrow$ safety($A$;$x$.$P$($x$) \& $Q$($x$))