template <class A, class B>
ostringstream & operator<<(ostringstream &o, const pair<A,B> &d) {
o << "<" << d.first << "," << d.second << ">";
template <class A, class B>
ostringstream & operator<<(ostringstream &o, const pair<A,B> &d) {
o << "<" << d.first << "," << d.second << ">";