Defined in header
The concept DerivedFrom<T, U> is satisfied if and only if
U is a class type that is either
T or a public and unambiguous base of
Despite the use of std::is_base_of and std::is_convertible in its description above,
DerivedFrom is not required to use it in its implementation. Thus, there need not be any subsumption relationship between DerivedFrom<T, U> and std::is_base_of<U,T>::value or std::is_convertible<std::remove_cv_t<T>*, std::remove_cv_t<U>*>::value.