int main() {
 euler_tour_tree ETT;
 auto a = ETT.make_node(1 << 0);
 auto b = ETT.make_node(1 << 1);
 auto c = ETT.make_node(1 << 2);
 auto ba = ETT.link(b, a);
 auto ca = ETT.link(c, a);
 ETT.cut(ba);
 // Now components are {a, c} and {b}.
 // Since b is a singleton component, there should be no child.
 cout << b->ch[0] << " " << b->ch[1] << endl; // expects 0 0
 // Something undefined happens...
 auto ab = ETT.link(a, b);
 cout << ETT.sum_in_component(a) << endl; // expects 0b111
 return 0;
}