std::experimental::ranges::InputIterator
From cppreference.com
 
 
 < cpp | experimental | ranges 
 
 
 C++ 
 Feature test macros (C++20)
 Concepts library (C++20)
 Metaprogramming library (C++11)
 Ranges library (C++20)
 Filesystem library (C++17)
 Concurrency support library (C++11)
 Execution control library (C++26)
Experimental 
 Filesystem library (filesystem TS)
 Library fundamentals (library fundamentals TS)
 Library fundamentals 2 (library fundamentals TS v2)
 Library fundamentals 3 (library fundamentals TS v3)
 Extensions for parallelism (parallelism TS)
 Extensions for parallelism 2 (parallelism TS v2)
 Extensions for concurrency (concurrency TS)
 Extensions for concurrency 2 (concurrency TS v2)
 Concepts (concepts TS)
 Ranges (ranges TS)
 Reflection (reflection TS)
 Mathematical special functions (special functions TR)
Iterators library 
    
    
    
   
    
 Iterator concepts
 Indirect callable concepts
 Common algorithm requirements
 Concept utilities
 Iterator utilities and operations
 Iterator traits
 Iterator adaptors
 Stream iterators
Defined in header 
 
 
<experimental/ranges/iterator> 
 template< class I >
 
 (ranges TS) 
concept bool InputIterator =
    Iterator<I> && Readable<I> &&
    requires { typename ranges::iterator_category_t<I>; } &&
The InputIterator concept is a refinement of Iterator, adding the requirement that the referenced values can be read (via Readable) and the requirement that the iterator category tag be present.
[edit] Notes
Unlike the input iterator requirements in the C++ standard, InputIterator in the Ranges TS does not require EqualityComparable.