[common.iter.types]

The nested typedef-name iterator_category of the specialization of iterator_traits for common_iterator<I, S> is defined if and only if iter_difference_t<I> is an integral type.

In that case, iterator_category denotes forward_iterator_tag if the qualified-id iterator_traits<I>::iterator_category is valid and denotes a type that models derived_from<forward_iterator_tag>; otherwise it denotes input_iterator_tag.

The remaining nested typedef-names of the specialization of iterator_traits for common_iterator<I, S> are defined as follows:

(2.1)
iterator_concept denotes forward_iterator_tag if I models forward_iterator; otherwise it denotes input_iterator_tag.
(2.2)
Let a denote an lvalue of type const common_iterator<I, S>.

If the expression a.operator->() is well-formed, then pointer denotes decltype(a.operator->().

Otherwise, pointer denotes void.