text: /* tra.h */
  
  struct node {
    int value;
    struct node *child_l;
    struct node *child_r;
  };
  struct node *create_node(int value);
  void pre_search_node(struct node *pointer);
  void ino_search_node(struct node *pointer);
  void pos_search_node(struct node *pointer);
  void add_node(struct node **pointer, struct node *new_node);
  