Concept proxiable_target

template <class T, class F>
concept proxiable_target = proxiable<observer-ptr<T>, observer_facade<F>>;

#include <proxy/proxy.h>

struct Runnable : pro::facade_builder                                    //
                  ::add_convention<pro::operator_dispatch<"()">, void()> //
                  ::build {};

int main() {
  auto fun = [] {};
  static_assert(pro::proxiable_target<decltype(fun), Runnable>);
  static_assert(!pro::proxiable_target<int, Runnable>);
}