comparison-common-type-with(C++20)

namespace std {
  template<class T, class U, class C = common_reference_t<const T&, const U&>>
  concept comparison-common-type-with-impl =
    same_as<common_reference_t<const T&, const U&>,
            common_reference_t<const U&, const T&>> &&
    requires {
      requires convertible_to<const T&, const C&> ||
               convertible_to<T, const C&>;
      requires convertible_to<const U&, const C&> ||
               convertible_to<U, const C&>;
    };

  template<class T, class U>
  concept comparison-common-type-with =
    comparison-common-type-with-impl<remove_cvref_t<T>, remove_cvref_t<U>>;
}