#include <iterator>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
 
template<typename T>
std::ostream &operator <<(std::ostream &os, const std::vector<T> &v) {
    using namespace std;
    for(size_t i = 0; i < v.size(); ++i)
    {
        os << v[i] << "\n";
    }
   // copy(v.begin(), v.end(), ostream_iterator<T>(os, "\n"));
    return os;
}
 
int main() {
    using namespace std;
    vector<string> v1;
    cout << v1;
    vector<vector<string> > v2;
    cout << v2;
    return 0;
}
 

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