#include <iostream>

int main()
{
    int a = 1, b = 1, c {1};

    auto m1 = [a, &b, &c]() mutable
    {
        std::cout << a << b << c << std::endl;
        auto m2 = [a, b, &c]() mutable
        {
            std::cout << a << b << c << '\n';
            a = 4; b = 4; c = 4;
        };

        a = 3; b = 3; c = 3;
        m2();
    };

    a = 2; b = 2; c = 2;

    m1();                             // calls m2() and prints 123
    std::cout << a << b << c << '\n'; // prints 234
}