template <class T>
vector<T>& operator-= (vector<T>& lhs, vector<T>& rhs) {
    for (vector<int>::iterator it=rhs.begin(); it!=rhs.end(); it!=rhs.end()?++it:it) {
        vector<int>::iterator el = std::find(lhs.begin(),lhs.end(),*it);
        if (el!=lhs.end()) lhs.erase(el);
    }	
    return lhs;
}