print_helper
static void print_helper(const struct node *, int);
print_helper(RB_RIGHT(n, node_link), indent + 4);
print_helper(RB_LEFT(n, node_link), indent + 4);
if (RB_ROOT(t)) print_helper(RB_ROOT(t), 0);
static void print_helper(const struct node *, int);
print_helper(RBT_RIGHT(n, node_link), indent + 4);
print_helper(RBT_LEFT(n, node_link), indent + 4);
if (RBT_ROOT(tree, t)) print_helper(RBT_ROOT(tree, t), 0);