append package:dlist

append xs ys is a DList obtained from the concatenation of the elements of xs and ys. <math>(1). append obeys the law:

toList (append xs ys) = toList xs ++ toList ys

append xs ys is a DNonEmpty obtained from the concatenation of the elements of xs and ys. <math>(1). append obeys the law:

toNonEmpty (append xs ys) = toNonEmpty xs <> toNonEmpty ys