The function {tt revappend} is similar to append, except that it adds the items in reverse order.
(Nth-Domain Revappend 3 List) (Nth-Domain Revappend 2 List) (Nth-Domain Revappend 1 List) (=> (Revappend ?L1 ?L2 ?New-List) (= ?New-List (If (Null ?L1) (If (List ?L2) ?L2) (Revappend (Rest ?L1) (Cons (First ?L1) ?L2)))))