$\forall$$A$, $B$:Type, $f$:($A$$\rightarrow$$B$), $L_{1}$, $L_{2}$:($A$ List).
\\[0ex]l\_subset($A$;$L_{1}$;$L_{2}$) $\Rightarrow$ l\_subset($B$;map($f$;$L_{1}$);map($f$;$L_{2}$))