Detecting Inheritance

template <typename T, typename U>
class Conversion
{
  ... as before ...
  public:
    enum { exists = sizeof(Test(MakeT())) == sizeof(Small) };
    enum { exists2Way = exists && Conversion<U,T>::exists};
    enum { sameType = false };
};

template <typename T>
class Conversion<T,T>
{
  public:
    enum { exists = 1, exists2Way = 1, sameType = 1
    };
};

#define SUPERSUBCLASS(T,U) (Conversion<const U*, const T*>::exists && \
                           !Conversion<const T*, const void*>::sameType)