1struct node {
 2  int data;
 3  struct node *next;
 4  struct node *prev;
 5};
 6
 7typedef struct node Node;
 8typedef void (Visitor)(Node *);
 9
10Node *initialize(int data);
11Node *add(Node *head, int data);
12Node *get(Node *from, int index);
13Node *reverse(Node *head);
14void inspect(Node *node);