package Deques istype Deque (<>)is tagged limited private;function Create return Deque;procedure Pop (D :access Deque);type Sequence is limited interface;type P_Deque is new Deque and Sequence with private;function Create return P_Deque;privatetype Deque is tagged limited null record;type P_Deque is new Deque and Sequence with null record;end Deques;