25 Iterators library [iterators]

25.3 Iterator requirements [iterator.requirements]

25.3.4 Iterator concepts [iterator.concepts] Concept input_or_output_iterator [iterator.concept.iterator]

The input_or_output_iterator concept forms the basis of the iterator concept taxonomy; every iterator models input_or_output_iterator.
This concept specifies operations for dereferencing and incrementing an iterator.
Most algorithms will require additional operations to compare iterators with sentinels ([iterator.concept.sentinel]), to read ([iterator.concept.input]) or write ([iterator.concept.output]) values, or to provide a richer set of iterator movements ([iterator.concept.forward], [iterator.concept.bidir], [iterator.concept.random.access]).
template<class I> concept input_or_output_iterator = requires(I i) { { *i } -> can-reference; } && weakly_incrementable<I>;
[Note 1: 
Unlike the Cpp17Iterator requirements, the input_or_output_iterator concept does not require copyability.
— end note]