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extern "C" int puts(char const*) noexcept;
using std::invoke_result_t;

// C++20 concepts
template<class T, class... As>
concept constructible_from = std::is_constructible_v<T, As...>;

template<class T>
concept move_constructible = constructible_from<T, T>;

template<class T>
concept copy_constructible =
   move_constructible<T> &&
   constructible_from<T, T const&>;

template<class A, class B>
concept derived_from = std::is_base_of_v<B, A>;

template<class F, class... As>
concept invocable = requires {
   typename invoke_result_t<F, As...>;
};

// Generic sender/receiver customization points and concept
// definitions, simplified (not to spec).
inline namespace _receiver_cpos_ {
   inline constexpr struct _set_value_fn_ {
       template<class R, class... As>
           requires requires(R&& r, As&&... as) {
               ((R&&)r).set_value((As&&) as...);
           }
       void operator()(R&& r, As&&... as) const
           noexcept(noexcept(((R&&)r).set_value((As&&) as...))) {
           ((R…

const struct {
   int a;
} kek;

void foo() {
   kek.a = 1;
}