Proposed resolution:

This wording is relative to N4910.

1. Modify [alg.rotate] as indicated:

   template<forward_range R, weakly_incrementable O>
     requires indirectly_copyable<iterator_t<R>, O>
     constexpr ranges::rotate_copy_result<borrowed_iterator_t<R>, O>
       ranges::rotate_copy(R&& r, iterator_t<R> middle, O result);
   

   -11- Effects: Equivalent to:

   return ranges::rotate_copy(ranges::begin(r), middle, ranges::end(r), std::move(result));