cpp/iterator/sentinel for

The concept specifies the relationship between an  type and a  type whose values denote a range. The exposition-only concept is described in.

Semantic requirements
Let and  be values of type  and, respectively, such that  denotes a range. is modeled only if:


 * is well-defined.
 * If then  is dereferenceable and  denotes a range.
 * is either modeled or not satisfied.

The domain of can change over time. Given an iterator and sentinel  such that  denotes a range and,  is not required to continue to denote a range after incrementing any iterator equal to  (and so  is no longer required to be well-defined after such an increment).