#include <iostream>
#include <cmath>

namespace foo {
    template<class T> 
    inline bool isnan (T x)
    { //!< \brief return true if floating-point type t is NaN (Not A Number).
       std::cout << "foo::isnan" << std::endl;
       return true;
    }
}

using foo::isnan;
using std::isnan;

int main () {
    std::cout << isnan(5.5f) << std::endl;
    return 0;
}