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#include <iostream>
#include <vector>

template <typename T>
std::vector<T>& operator +(const std::vector<T>& vector1, const std::vector<T>& vector2) {
    std::vector<T> newVec;
    newVec.insert(vector1.end(), vector2.begin(), vector2.end());
    return newVec;
}

template <typename T>
std::vector<T>& operator +=(std::vector<T>& vector1, const std::vector<T>& vector2) {
    vector1.insert(vector1.end(), vector2.begin(), vector2.end());
    return vector1;
}


using namespace std;

int main() {
    print(std::vector<double> {6.7, -12.3, 5} + std::vector<double> {0.5, -2.7, 19});
    std::vector<double> vector {6.7, -12.3, 5};
    print((vector += std::vector<double> {0.5, -2.7}) += std::vector<double> {19});
    print(vector);

}