p->next=s;s->prior=p;p->next->prior=s;s->next=p->next

p->next->prior=s;p->next=s;s->prior=p;s->next=p->next

s->prior=p;s->next=p->next;p->next=s;p->next->prior=s

s->prior=p;s->next=p->next;p->next->prior=s;p->next=s