$\forall$$i$:Top, $L$:Top List, $A$:Top. R{-}da($\oplus$$x$$\in$$L$.$A$($x$);$i$) $\sim$ reduce($\lambda$$x$,${\it da}$. R{-}da($A$($x$);$i$) $\oplus$ ${\it da}$;;$L$)