Upcasting facility refactored by adding additional alias templates

src/include/units/unit.h

@@ -49,7 +49,6 @@ namespace units {
   template<typename T>
   concept bool Unit =
       std::is_empty_v<T> &&
-      detail::is_unit<typename T::base_type> &&
-      std::experimental::ranges::DerivedFrom<T, typename T::base_type>;
+      detail::is_unit<upcast_from<T>>;
 
 }  // namespace units