\begin{tabbing}
$\forall$$A$, $B$:Type, $L_{2}$:(Id$\times$($A$$\rightarrow$$B$$\rightarrow$(Top List))) List, $L$:(Top$\times$Id$\times$Top) List, ${\it tg}$:Id, $a$:$A$, $b$:$B$.
\\[0ex]\{\=map($\lambda$$x$.2of($x$);$L$)\+
\\[0ex]$=$
\\[0ex]concat(map($\lambda$${\it tgf}$.map($\lambda$$x$.$\langle$1of(${\it tgf}$)$,\,$$x$$\rangle$;2of(${\it tgf}$)($a$,$b$));$L_{2}$))
\\[0ex]$\in$ (Id$\times$Top) List
\\[0ex]$\Rightarrow$ $\neg$(${\it tg}$ $\in$ map($\lambda$$p$.1of($p$);$L_{2}$))
\\[0ex]$\Rightarrow$ filter($\lambda$${\it ms}$.1of(2of(${\it ms}$)) = ${\it tg}$;$L$) $=$ nil $\in$ (Top$\times$Id$\times$Top) List\}
\-
\end{tabbing}