#include <string>
#include <memory>
#include <iostream>
namespace X
{
class S;
}
std::string r(X::S &s);
namespace X
{
class S
{
friend std::string (::r)(X::S &s);
std::unique_ptr<std::istream> s_;
};
}
std::string r(X::S &s)
{
auto& x = s.s_;
return "";
}
int main(void) {}
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