// UZUPEŁNIJ 1
std::ostream& operator(std::ostream& s, const is_printable& o);

int main() {
    A a = {"Tekst"}; B b {123};
    std::cout << "a:\t" << a << "; b:\t" << b << "\n";
    is_printable& a_r = a; is_printable& b_r = b;
    std::cout << "a_r:\t" << a_r << "; b_r:\t" << b_r << "\n";
}