#include <iostream>
#include <string>

template <class T> concept bool Addable = requires (T t) { t + t; };

int main()
{
	int x = 1, y = 2;
	Addable z = x + y;

	std::string a = "a", b = "b";
	Addable c = a + b;

	std::cout << x << " + " << y << " = " << z << std::endl
	          << a << " + " << b << " = " << c << std::endl;
}