struct rotate_fn{template<std::permutable I,std::sentinel_for<I> S>constexprranges::subrange<I>        operator()(I first, I middle, S last)const{if(first== middle){auto last_it=ranges::next(first, last);return{last_it, last_it};}if(middle== last)return{std::move(first), std::move(middle)}; ifconstexpr(std::bidirectional_iterator<I>){ranges::reverse(first, middle);auto last_it=ranges::next(first, last);ranges::reverse(middle, last_it); ifconstexpr(std::random_access_iterator<I>){ranges::reverse(first, last_it);return{first+(last_it- middle), std::move(last_it)};}else{auto mid_last= last_it;do{ranges::iter_swap(first,--mid_last);++first;}while(first!= middle&& mid_last!= middle);ranges::reverse(first, mid_last); if(first== middle)return{std::move(mid_last), std::move(last_it)};elsereturn{std::move(first), std::move(last_it)};}}else{// I is merely a forward_iteratorauto next_it= middle;do{// rotate the first cycleranges::iter_swap(first, next_it);++first;++next_it;if(first== middle)                    middle= next_it;}while(next_it!= last); auto new_first= first;while(middle!= last){// rotate subsequent cycles                next_it= middle;do{ranges::iter_swap(first, next_it);++first;++next_it;if(first== middle)                        middle= next_it;}while(next_it!= last);} return{std::move(new_first), std::move(middle)};}} template<ranges::forward_range R>    requiresstd::permutable<ranges::iterator_t<R>>constexprranges::borrowed_subrange_t<R>        operator()(R&& r,ranges::iterator_t<R> middle)const{return(*this)(ranges::begin(r), std::move(middle),ranges::end(r));}}; inlineconstexpr rotate_fn rotate{};