• p->next=q;q->prior=p;p->next->prior=q;q->next=q;
  • p->next=q;p->next->prior=q;q->prior=p;q->next=p->next;
  • q->prior=p;q->next=p->next;p->next->prior=q;p->next=q;
  • q->next=p->next;q->prior=;p->next=q;p->next=q;
  •