void deq_pushBack(dequeue q, void *element){ create_and_link(element, q->tail->prev, q->tail); }
void dq_enq_back(dqueue q, void *element) { create_and_link(element, q -> sentinel -> prev, q -> sentinel); }
void deq_pushFront(dequeue q, void *element) { create_and_link(element, q->head, q->head->next); }
void dq_enq_front(dqueue q, void *element) { create_and_link(element, q -> sentinel, q -> sentinel -> next); }