Dear all, As suggested by several people, I have started to rely on range_difference<T>::type in all places of the library. I have also updated the docs w.r.t new concepts and are working on polishing them. 1.35 will introduce a new function template< class T > BOOST_DEDUCED_TYPENAME range_difference<T>::type size( const T& r ); that requires T to be a random access range. I also want to put a post-condition saying "result >= 0", but was a bit in doubt when I read the standards wording for std::distance(): "template<class InputIterator> typename iterator_traits<InputIterator>::difference_type distance(InputIterator first, InputIterator last); 4 Effects: Returns the number of increments or decrements needed to get from first to last. 5 Requires: last shall be reachable from first." How can one ever use decrements to get from first to last? Any comments? -Thorsten