operator==,!=,<,<=,>,>=(std::experimental::observer_ptr)
From cppreference.com
                    
                                        
                    < cpp | experimental | observer ptr
                    
                                                            
                    |   template<class W1, class W2> 
bool operator==(const observer_ptr<W1>& p1, const observer_ptr<W2>& p2);  | 
(1) | (library fundamentals TS v2) | 
|   template<class W1, class W2> 
bool operator!=(const observer_ptr<W1>& p1, const observer_ptr<W2>& p2);  | 
(2) | (library fundamentals TS v2) | 
|   template<class W> 
bool operator==(const observer_ptr<W>& p, std::nullptr_t);  | 
(3) | (library fundamentals TS v2) | 
|   template<class W> 
bool operator==(std::nullptr_t, const observer_ptr<W>& p);  | 
(4) | (library fundamentals TS v2) | 
|   template<class W> 
bool operator!=(const observer_ptr<W>& p, std::nullptr_t);  | 
(5) | (library fundamentals TS v2) | 
|   template<class W> 
bool operator!=(std::nullptr_t, const observer_ptr<W>& p);  | 
(6) | (library fundamentals TS v2) | 
|   template<class W1, class W2> 
bool operator<(const observer_ptr<W1>& p1, const observer_ptr<W2>& p2);  | 
(7) | (library fundamentals TS v2) | 
|   template<class W1, class W2> 
bool operator>(const observer_ptr<W1>& p1, const observer_ptr<W2>& p2);  | 
(8) | (library fundamentals TS v2) | 
|   template<class W1, class W2> 
bool operator<=(const observer_ptr<W1>& p1, const observer_ptr<W2>& p2);  | 
(9) | (library fundamentals TS v2) | 
|   template<class W1, class W2> 
bool operator>=(const observer_ptr<W1>& p1, const observer_ptr<W2>& p2);  | 
(10) | (library fundamentals TS v2) | 
Compares the pointer values of two observer_ptrs, or a observer_ptr and nullptr.
1-2) Equality comparison for two 
observer_ptrs
3-6) Equality comparison for an 
observer_ptr and nullptr.
7-10) Ordered comparison for two 
observer_ptrs[edit] Parameters
| p, p1, p2 | - |   observer_ptrs to compare
 | 
[edit] Return value
1) p1.get() == p2.get()
2) !(p1 == p2)
3-4) !p
5-6) (bool)p
7) std::less<W3>()(p1.get(), p2.get()), where W3 is the composite pointer type of W1* and W2*
8) p2 < p1
9) !(p2 < p1)
10) !(p1 < p2)
[edit] Exceptions
3-6)
noexcept specification:  
noexcept