void RC reverse (Tree_node WR *node)
{
  void walk_left_right (Tree_node WR *node)
  {
    if (node->left) reverse (node->left);
    if (node->right) reverse (node->right);
  }

  walk_left_right (node);

  Tree_node *n = node->left;

  node->left = node->right;
  node->right = n;
}
