Looking the "possible" implementation section of std::same_as something strikes me as odd:
namespace detail {
template< class T, class U >
concept SameHelper = std::is_same_v<T, U>;
}
template< class T, class U >
concept same_as = detail::SameHelper<T, U> && detail::SameHelper<U, T>;
The check for type equality is done twice, once as T==U and the second as U==T. Given that equailty is symmetric by nature, why is the extra check needed?