moveEarlier :: ListZip a -> Maybe (ListZip a)
moveEarlier (ListZip late a (a' :> early)) =
    Just (ListZip (late :< a) a' early)
moveEarlier :: ListZip a -> Maybe (ListZip a)
moveEarlier (ListZip late a (a' :> early)) =
    Just (ListZip (late :< a) a' early)
moveEarlier (ListZip late a (a' :> early)) =
    Just (ListZip (late :< a) a' early)