39   requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
56     requires forward_range<_D2>  in empty()
63     requires forward_range<const _D2>  in empty()
71     requires requires (_D2& __t) { ranges::empty(__t); }  in requires()  function
79     requires requires (const _D2& __t) { ranges::empty(__t); }  in requires()  function
87     requires contiguous_iterator<iterator_t<_D2>>  in data()
95     requires range<const _D2> && contiguous_iterator<iterator_t<const _D2>>  in data()
103     requires forward_range<_D2> && sized_sentinel_for<sentinel_t<_D2>, iterator_t<_D2>>  in size()
111 …requires forward_range<const _D2> && sized_sentinel_for<sentinel_t<const _D2>, iterator_t<const _D…  in size()
119     requires forward_range<_D2>  in decltype()
129     requires forward_range<const _D2>  in decltype()
139     requires bidirectional_range<_D2> && common_range<_D2>  in decltype()
149     requires bidirectional_range<const _D2> && common_range<const _D2>  in decltype()