45     node* tail;  variable
50     Map() : head( NULL ), tail ( NULL ),tmp(head),size_of_list(0) {}  in Map()
52         return ( !head || !tail );  in empty()
148     tail = new node(data, data2,tail, NULL);  in insert()
150     if ( tail->prev )  in insert()
151         tail->prev->next = tail;  in insert()
154         head = tail;  in insert()
171         if ((head == tail) && (head->data == d)) {  in erase()
174             head = tail = NULL;  in erase()
190         if ((tmp == tail) && (tmp->data ==d)) {  in erase()
195             tail = prevnode;  in erase()
232     tail = head = NULL;  in eraseall()