$\forall$$T$:Type, $L$:$T$ List, $f$:($T$$\rightarrow$System), $x$:$T$.
\\[0ex]($\forall$$x$,$y$$\in$$L$.$f$($x$) $\parallel$ $f$($y$)) $\Rightarrow$ ($x$ $\in$ $L$) $\Rightarrow$ $f$($x$) $\subseteq$ $\oplus$(map($\lambda$$x$.$f$($x$);$L$))