#include <iostream>
using namespace std;
 
template <typename F>
struct curry_impl {
    F f;
	curry_impl(F f) : f(f) {}
	template <typename A>
	struct inner {
		F f; A a;
		inner(F f, A a) : f(f), a(a) {}
		template <typename B>
		auto operator () (B b) -> decltype(f(a, b)) {
			return f(a, b);
		}
	};
	template <typename A>
	auto operator () (A a) -> inner<A> {
		return inner<A>(f, a);
	}
};
template <typename F>
curry_impl<F> curry(F f) {
	return curry_impl<F>(f);
}
 
int main() {
    cout << curry([](int x, int y) { return x + y; })(21)(21) << endl;
}

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