std::ranges::join_view<V>::iterator<Const>::operator++,--
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   constexpr /*iterator*/& operator++();  | 
(1) | (since C++20) | 
|   constexpr void operator++( int );  | 
(2) | (since C++20) | 
|   constexpr /*iterator*/ operator++( int )     requires /*ref-is-glvalue*/ && ranges::forward_range<Base> &&  | 
(3) | (since C++20) | 
|   constexpr iterator& operator--()     requires /*ref-is-glvalue*/ && ranges::bidirectional_range<Base> &&  | 
(4) | (since C++20) | 
|   constexpr /*iterator*/ operator--( int )     requires /*ref-is-glvalue*/ && ranges::bidirectional_range<Base> &&  | 
(5) | (since C++20) | 
Increments or decrements the underlying iterator.
Let inner_ and outer_ be the underlying iterators, and parent_ be the pointer to parent ranges::join_view, the constant /*ref-is-glvalue*/ be std::is_reference_v<ranges::range_reference_t<Base>>.
1) Let /*inner-range*/ be:
- *outer_, if /*ref-is-glvalue*/ == true;
 - *parent_->inner_ otherwise.
 
Equivalent to:
auto&& inner_rng = /*inner-range*/; if (++inner_ == ranges::end(inner_rng)) { ++outer_; satisfy(); } return *this;
2) Equivalent to: ++*this.
3) Equivalent to:
auto tmp = *this; ++*this; return tmp;
4) Equivalent to:
if (outer_ == ranges::end(parent_->base_)) inner_ = ranges::end(*--outer_); while (inner_ == ranges::begin(*outer_)) inner_ = ranges::end(*--outer_); --inner_; return *this;
5) Equivalent to: 
auto tmp = *this; --*this; return tmp;
Parameters
(none)
Return value
1,4) *this
2) (none)
3,5) a copy of *this that was made before the change.