I'm troubleshooting counting_iterator_test.hpp. In particular: FILE: counting_iterator_test.cpp class my_int2 { public: ... typedef std::bidirectional_iterator_tag iterator_category; }; FILE: counting_iterator.hpp template <class Incrementable, class CategoryOrTraversal, class Difference> struct counting_iterator_base { typedef typename detail::ia_dflt_help< CategoryOrTraversal , mpl::apply_if< is_numeric<Incrementable> , mpl::identity<random_access_traversal_tag> , iterator_traversal<Incrementable> > >::type traversal; ... } The class my_int2 is passed as parameter "Incrementable" to counting_iterator_base, but is failing the is_numeric test so my_int2 is just a bidirectional iterator (see mpl::apply_if above). If it passes the is_numeric test, then it's a random access traversal tag. The way it passes the is_numeric test is to specialize std::numeric_limits like so: template <> class std::numeric_limits<my_int2> { public: static bool const is_specialized = false; }; But I don't find that in the source. It appears that aC++ doing the right thing, but I know I'm wrong. Could somebody please help?? Thanks! -Jerry