extern edge_t *new_edge(void);
extern void free_edge(edge_t *);
extern void edge_add(edge_t *);
extern void edge_del(edge_t *);
extern edge_t *lookup_edge(struct node_t *, struct node_t *);
extern edge_t *new_edge(void);
extern void free_edge(edge_t *);
extern void edge_add(edge_t *);
extern void edge_del(edge_t *);
extern edge_t *lookup_edge(struct node_t *, struct node_t *);