libstdc++/user/a13595.html

template<typename _Tp, typename _Up>

concept std::common_with =  same_as<common_type_t<_Tp, _Up>, common_type_t<_Up, _Tp>>

      && requires {

        static_cast<common_type_t<_Tp, _Up>>(std::declval<_Tp>());

        static_cast<common_type_t<_Tp, _Up>>(std::declval<_Up>());

      }

      && common_reference_with<add_lvalue_reference_t<const _Tp>,

                               add_lvalue_reference_t<const _Up>>

      && common_reference_with<add_lvalue_reference_t<common_type_t<_Tp, _Up>>,

                               common_reference_t<

                                 add_lvalue_reference_t<const _Tp>,

                                 add_lvalue_reference_t<const _Up>>>

std::add_lvalue_reference_t
typename add_lvalue_reference< _Tp >::type add_lvalue_reference_t
Alias template for add_lvalue_reference.
Definition type_traits:1665

std::common_type_t
typename common_type< _Tp... >::type common_type_t
Alias template for common_type.
Definition type_traits:2613

std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2384

std::same_as
[concept.same], concept same_as
Definition concepts:63

std::common_reference_with
[concept.commonref], concept common_reference_with
Definition concepts:78

std::common_with
[concept.common], concept common_with
Definition concepts:85