concept ranges::random_access_iterator_ =     
requires( I i, iter_difference_t<I> n ) {  i + n,             n + i,             i - n,             i += n,             i -= n,             concepts::requires_<same_as<
decltype(i + n), I>>,             concepts::requires_<same_as<
decltype(n + i), I>>,             concepts::requires_<same_as<
decltype(i - n), I>>,             concepts::requires_<same_as<
decltype(i += n), I&>>,             concepts::requires_<same_as<
decltype(i -= n), I&>>,             concepts::requires_<same_as<
decltype(i[n]), iter_reference_t<I>>> ; }