add_label
add_label(&$2->labels, $1);
add_label(&target->labels, $2);
add_label(&$2->labels, $1);
add_label(&$2->labels, $1);
void add_label(struct label **labels, char *label);
add_label(&labeled_node->labels, p->name);
add_label(&old_node->labels, l->label);
add_label(&old_prop->labels, l->label);