$\vdash$  $\forall$$T$:Type, $L_{1}$, $L_{2}$:($T$ List). $L_{1}$ $\subseteq$ $L_{2}$ $\Rightarrow$ ($\forall$$x$, $y$:$T$. adjacent($T$;$L_{1}$;$x$;$y$) $\Rightarrow$ $x$ before $y$ $\in$ $L_{2}$)