import java.util.Iterator;

public interface Deque<Item> extends Iterable<Item>{

     boolean isEmpty();           // returns true if the deque is empty, false otherwise
     int size() ;                 // returns the number of items in the deque
     void pushLeft(Item item);    // pushes an item onto the left side of the deque
     void pushRight(Item item);   // pushes an item onto the right side of the deque
     Item popLeft();              // pops the left-most item off the deque and returns it
     Item popRight();             // pops the right-most item off the deque and returns it
}